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Comprehensive Income (Loss) - Schedule of AOCI Components (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Mar. 31, 2021 | Jun. 30, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period | $ 9,093 | $ 8,876 | $ 8,876
Changes in fair value | 186 |  | 279
Reclassification to earnings | 10 |  | (19)
Balance at end of period | 9,688 | $ 9,093 | $ 9,688
Accounting Standards Update [Extensible Enumeration] |  | Accounting Standards Update 2016-01 | Accounting Standards Update 2016-01
Cumulative effect of adopting Accounting Standards Update No. 2016-01, Financial Instruments (See Note 1) |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period |  | $ 0 | $ 0
Accumulated other comprehensive income (loss) |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period | (60) | (105) | (105)
Balance at end of period | 136 | (60) | 136
Accumulated other comprehensive income (loss) | Cumulative effect of adopting Accounting Standards Update No. 2016-01, Financial Instruments (See Note 1) |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period |  | (19) | (19)
Fuel and Interest Rate Derivatives | Fuel derivatives |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period | 12 | (119) | (119)
Changes in fair value | 250 |  | 359
Reclassification to earnings | 12 |  | 34
Balance at end of period | 274 | 12 | 274
Fuel and Interest Rate Derivatives | Interest rate derivatives |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period | (53) | (66) | (66)
Changes in fair value | (7) |  | 5
Reclassification to earnings | 1 |  | 2
Balance at end of period | (59) | (53) | (59)
Defined benefit plan items |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period | (43) | (43) | (43)
Balance at end of period | (43) | (43) | (43)
Other |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period |  | 91 | 91
Reclassification to earnings |  |  | (60)
Balance at end of period | 0 |  | 0
Other | Cumulative effect of adopting Accounting Standards Update No. 2016-01, Financial Instruments (See Note 1) |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period |  | (31) | (31)
Deferred tax |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period | 24 | 32 | 32
Changes in fair value | (57) |  | (85)
Reclassification to earnings | (3) |  | 5
Balance at end of period | $ (36) | 24 | (36)
Deferred tax | Cumulative effect of adopting Accounting Standards Update No. 2016-01, Financial Instruments (See Note 1) |  |  |
AOCI Attributable to Parent, Net of Tax [Roll Forward] |  |  |
Balance at beginning of period |  | $ 12 | $ 12

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