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Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | $ 26,001 | $ 26,882 | $ 34,569
Other comprehensive income (loss) before reclassification adjustments, pretax | (915) | (610) | (692)
Tax | 284 | 161 | (24)
Other comprehensive income (loss) before reclassification adjustments, net of taxes | (631) | (449) | (716)
Reclassification adjustments, pretax | 253 | (239) | 424
Tax | (63) | 40 | (69)
Reclassification adjustments, net of taxes | 190 | (199) | 355
Other comprehensive income (loss), net of taxes | (441) | (648) | (361)
Adoption of ASU 2018-02 |  |  | (266)
Ending Balance | 25,404 | 26,001 | 26,882
Cumulative Effect, Period of Adoption, Adjustment |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | 48
Derivatives |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | 31 | 166 | (108)
Other comprehensive income (loss) before reclassification adjustments, pretax | (383) | 86 | 228
Tax | 84 | (15) | (55)
Other comprehensive income (loss) before reclassification adjustments, net of taxes | (299) | 71 | 173
Reclassification adjustments, pretax | 2 | (261) | 157
Tax | 0 | 55 | (33)
Reclassification adjustments, net of taxes | 2 | (206) | 124
Other comprehensive income (loss), net of taxes | (297) | (135) | 297
Adoption of ASU 2018-02 |  |  | (23)
Ending Balance | (266) | 31 | 166
Derivatives | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01 |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | 0
Investments |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | 18 | (78) | (61)
Other comprehensive income (loss) before reclassification adjustments, pretax | 3 | 140 | (108)
Tax | 0 | 0 | 1
Other comprehensive income (loss) before reclassification adjustments, net of taxes | 3 | 140 | (107)
Reclassification adjustments, pretax | (21) | (44) | 97
Tax | 0 | 0 | 0
Reclassification adjustments, net of taxes | (21) | (44) | 97
Other comprehensive income (loss), net of taxes | (18) | 96 | (10)
Adoption of ASU 2018-02 |  |  | 1
Ending Balance | 0 | 18 | (78)
Investments | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01 |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | (8)
Employee Benefit Plans |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | (4,261) | (3,556) | (2,787)
Other comprehensive income (loss) before reclassification adjustments, pretax | (599) | (948) | (728)
Tax | 111 | 192 | 169
Other comprehensive income (loss) before reclassification adjustments, net of taxes | (488) | (756) | (559)
Reclassification adjustments, pretax | 272 | 66 | 170
Tax | (63) | (15) | (36)
Reclassification adjustments, net of taxes | 209 | 51 | 134
Other comprehensive income (loss), net of taxes | (279) | (705) | (425)
Adoption of ASU 2018-02 |  |  | (344)
Ending Balance | (4,540) | (4,261) | (3,556)
Employee Benefit Plans | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01 |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | 0
Pension Plan Net Loss |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Pension and other postretirement benefit plans, net loss and prior service (credit) included in AOCI | 5,400 | 5,100 |
Other Postretirement Benefit Plan Net Gain |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Pension and other postretirement benefit plans, net loss and prior service (credit) included in AOCI | (391) | (247) |
Pension Plan Prior Service Credit |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Pension and other postretirement benefit plans, net loss and prior service (credit) included in AOCI | (255) | (263) |
Other Postretirement Benefit Plan Prior Service Credit |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Pension and other postretirement benefit plans, net loss and prior service (credit) included in AOCI | (244) | (305) |
Cumulative Translation Adjustment |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | (1,981) | (2,077) | (1,954)
Other comprehensive income (loss) before reclassification adjustments, pretax | 64 | 112 | (84)
Tax | 89 | (16) | (139)
Other comprehensive income (loss) before reclassification adjustments, net of taxes | 153 | 96 | (223)
Reclassification adjustments, pretax | 0 | 0 | 0
Tax | 0 | 0 | 0
Reclassification adjustments, net of taxes | 0 | 0 | 0
Other comprehensive income (loss), net of taxes | 153 | 96 | (223)
Adoption of ASU 2018-02 |  |  | 100
Ending Balance | (1,828) | (1,981) | (2,077)
Cumulative Translation Adjustment | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01 |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | 0
Accumulated Other Comprehensive Income (Loss) |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | (6,193) | (5,545) | (4,910)
Ending Balance | $ (6,634) | $ (6,193) | (5,545)
Accumulated Other Comprehensive Income (Loss) | Cumulative Effect, Period of Adoption, Adjustment |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | (274)
Accumulated Other Comprehensive Income (Loss) | Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-01 |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | $ (8)

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