Slicers (applies to each fact value in each table cell)

Reporting Entity [Axis]

0000277948 (http://www.sec.gov/CIK)

Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]	Period [Axis]
	2015-12-26 - 2016-12-30
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Summary of Participants	In order to perform this valuation, the actuaries are provided with the details of the population covered at the beginning of the year, summarized in the table below, and projects that population forward to the end of the year.   Summary of Participants as of   January 1, 2016   Pension Plans   Post-retirement Medical Plan Active Employees 4,823   1,139 Retirees and Beneficiaries 12,018   11,893 Other(a) 3,853   54 Total 20,694   13,086 (a) For pension plans, the other category consists mostly of terminated but vested former employees.  For post-retirement plans, the other category consists of employees on long-term disability that have not yet retired.
Schedule of Future Expected Benefit Payments	Future expected benefit payments are as follows:   Expected Cash Flows (Dollars in Millions) Pension Benefits   Post-retirement Benefits 2017 $ 183   $ 39 2018 185   28 2019 184   26 2020 182   24 2021 182   22 2022-2026 904   86 Total $ 1,820   $ 225
Schedule of Allocation of Plan Assets	The distribution of pension plan assets as of the measurement date is shown in the table below, and these assets are netted against the pension liabilities on the balance sheet.   December 2016   December 2015       Percent of       Percent of (Dollars in Millions) Amount   Total Assets   Amount   Total Assets Equity $ 1,806   71 %   $ 1,626   70 % Fixed Income 665   26   641   28 Cash and Cash Equivalents 68   3   42   2 Total $ 2,539   100 %   $ 2,309   100 %
Schedule of Changes in Benefit Obligation and Fair Value of Plan Assets	Changes in benefit obligation and the fair value of plan assets for the 2016 and 2015 calendar plan years are as follows:   Pension Benefits   Post-retirement Benefits   Plan Year   Plan Year   Plan Year   Plan Year (Dollars in Millions) 2016   2015   2016   2015 Actuarial Present Value of Benefit Obligation               Accumulated Benefit Obligation $ 2,717   $ 2,672   N/A   N/A Projected Benefit Obligation 2,871   2,860   $ 274   $ 314                 Change in Projected Benefit Obligation:               Projected Benefit Obligation at Beginning of Plan Year $ 2,860   $ 3,002   $ 314   $ 340 Service Cost 48   45   2   2 Interest Cost 119   116   12   12 Plan Participants' Contributions —   —   6   7 Workforce Reduction Program/Curtailment —   7   —   — Actuarial Loss (Gain) 20   (110 )   (22 )   (7 ) Benefits Paid (176 )   (200 )   (38 )   (40 ) Benefit Obligation at End of Plan Year $ 2,871   $ 2,860   $ 274   $ 314                 Change in Plan Assets:               Fair Value of Plan Assets at Beginning of Plan Year $ 2,309   $ 2,504   $ —   $ — Actual Return on Plan Assets 139   (9 )   —   — Qualified Employer Contributions 250   —   —   — Non-qualified Employer Contributions 17   14   32   33 Plan Participants' Contributions —   —   6   7 Benefits Paid (176 )   (200 )   (38 )   (40 ) Fair Value of Plan Assets at End of Plan Year 2,539   2,309   —   — Funded Status at End of Plan Year $ (332 )   $ (551 )   $ (274 )   $ (314 )
Schedule of Amount Recognized in Balance Sheet	Amounts related to pension and post-retirement benefits recorded in other long-term assets, labor and fringe benefits payable and other long-term liabilities on the balance sheet are as follows:   Pension Benefits   Post-retirement Benefits   December   December   December   December (Dollars in Millions) 2016   2015   2016   2015 Amounts Recorded in Consolidated               Balance Sheets:               Long-term Assets (a) $ 9   $ 9   $ —   $ — Current Liabilities (15 )   (15 )   (39 )   (36 ) Long-term Liabilities (326 )   (545 )   (235 )   (278 ) Net Amount Recognized in               Consolidated Balance Sheets $ (332 )   $ (551 )   $ (274 )   $ (314 ) (a) Long-term assets as of December 2016 and 2015 relate to one of the qualified pension plans whose assets exceed projected benefit obligations.
Benefit Obligations in Excess of Plan Assets	At December 2016, the status of CSX plans only with a net liability is disclosed below. The total fair value of all plans as of December 2016 was $2.5 billion, which includes the qualified pension plans with net assets.   Aggregate   (Dollars in Millions) Fair Value Aggregate Benefit Obligations in Excess of Plan Assets of Plan Assets Benefit Obligation Projected Benefit Obligation $ 2,506 $ (2,847 ) Accumulated Benefit Obligation 2,506 (2,692 )
Schedule of Net Benefit Expense	The following table describes the components of expense/(income) related to net benefit expense recorded in labor and fringe on the income statement.   Pension Benefits Fiscal Years   Post-retirement Benefits Fiscal Years (Dollars in Millions) 2016   2015   2014   2016   2015   2014 Service Cost $ 48   $ 45   $ 44   $ 2   $ 2   $ 3 Interest Cost 119   116   123   12   12   13 Expected Return on Plan Assets (157 )   (162 )   (166 )   —   —   — Amortization of Net Loss 48   70   57   3   4   5 Amortization of Prior Service Cost —   —   —   —   (1 )   (1 ) Net Periodic Benefit Expense 58   69   58   17   17   20 Special Termination Benefits - Workforce Reduction Program/Curtailment(a) —   7   27   —   —   8 Settlement Gain(b) (1 )   (2 )   (1 )   —   —   — Total Expense $ 57   $ 74   $ 84   $ 17   $ 17   $ 28 (a) Special termination benefits are charges in 2015 and 2014 that resulted from a management workforce reduction program initiated in 2014. For further information regarding the program, see Note 1. Nature of Operations and Significant Accounting Policies. (b) Settlement gains were recognized as one of the pension plan's lump-sum payments to retirees with insignificant balances exceeded the sum of the service cost and interest cost recognized.  The gain is the recognition of a portion of its accumulated other comprehensive income related to that plan
Schedule of Pre-tax Change in Other Comprehensive Loss (Income)	The following table shows the pre-tax change in other comprehensive loss (income) attributable to the components of net expense and the change in benefit obligation for CSX for pension and other post-employment benefits. (Dollars in Millions) Pension Benefits   Post-retirement Benefits Components of Other Comprehensive December   December   December   December Loss (Income) 2016   2015   2016   2015 Recognized in the balance sheet               Losses (Gains) $ 38   $ 60   $ (22 )   $ (7 ) Expense (Income) recognized in the income statement               Amortization of net losses (a) $ 48   $ 70   $ 3   $ 4 Settlement gain (1 )   (2 )   —   — Amortization of prior service costs —   —   —   (1 ) (a) Amortization of net losses estimated to be expensed for 2017 is approximately $43 million for pension benefits.
Schedule of Pre-tax Amounts to be Amortized that are Included in Accumulated Other Comprehensive Loss	As of December 2016, the balances of pre-tax amounts to be amortized that are included in accumulated other comprehensive loss (a component of shareholders’ equity) are as follows:   Pension Benefits   Post-retirement Benefits Losses $ 891   $ 24 Prior Service Costs (Credits) —   — Total $ 891   $ 24
Schedule of Weighted-Average Assumptions Used	eighted averages of assumptions used by the Company to value its pension and post-retirement obligations were as follows:   Pension Benefits   Post-retirement Benefits   2016   2015   2016   2015 Expected Long-term Return on Plan Assets:               Benefit Cost for Current Plan Year 7.00 %   7.25 %   N/A   N/A Benefit Cost for Subsequent Plan Year 6.75 %   7.00 %   N/A   N/A                 Discount Rates:               Benefit Cost for Plan Year 4.30 %   4.00 %   3.85 %   3.60 % Benefit Obligation at End of Plan Year 4.08 % (a)  4.30 %   3.71 %   3.85 %                 Salary Scale Inflation 4.60 %   4.60 %   N/A   N/A