The following table summarizes the changes in impairment loss of doubtful accounts:
2017 | 2016 | |||||||
Million | Million | |||||||
As of January 1 |
5,762 | 6,549 | ||||||
Impairment loss recognized |
3,415 | 3,797 | ||||||
Accounts receivable written off |
(3,509 | ) | (4,584 | ) | ||||
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As of December 31 |
5,668 | 5,762 | ||||||
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