The following table shows our property and equipment: | | | | | | | | | | | December 31, | (in millions, except for estimated useful life) | Estimated Useful Life | 2013 | 2012 | Flight equipment | 21-30 years | $ | 23,373 |
| $ | 21,481 |
| Ground property and equipment | 3-40 years | 4,596 |
| 4,254 |
| Flight and ground equipment under capital leases | Shorter of lease term or estimated useful life | 1,296 |
| 1,381 |
| Advance payments for equipment | | 381 |
| 253 |
| Less: accumulated depreciation and amortization(1) | | (7,792 | ) | (6,656 | ) | Total property and equipment, net | | $ | 21,854 |
| $ | 20,713 |
|
(1) Includes accumulated amortization for flight and ground equipment under capital leases in the amount of $657 million and $653 million at December 31, 2013 and 2012, respectively. |