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Basis of Presentation (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Jun. 30, 2021 | Mar. 31, 2021 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Payroll support and voluntary Employee programs, net | $ 776 |  | $ 149 | $ 2,963 | $ 933 |  |  |  |  |
Other (gains) losses, net | (29) |  | (35) | 32 | (95) |  |  |  |  |
Decrease in AOCI | 10,250 | $ 8,876 | 9,769 | 10,250 | 9,769 | $ 9,688 | $ 9,093 | $ 10,878 | $ 9,075 | $ 9,832
Accumulated other comprehensive income (loss) |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in AOCI | 267 | (105) | (102) | 267 | (102) | 136 | (60) | (130) | (186) | (61)
Retained earnings |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in AOCI | 15,706 | 14,777 | $ 15,685 | 15,706 | $ 15,685 | $ 15,260 | $ 14,912 | $ 16,842 | $ 17,757 | $ 17,945
Cumulative Effect, Period of Adoption, Adjustment |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in AOCI |  | 0 |  |  |  |  |  |  |  |
Cumulative Effect, Period of Adoption, Adjustment | Accumulated other comprehensive income (loss) |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in AOCI |  | (19) |  |  |  |  |  |  |  |
Cumulative Effect, Period of Adoption, Adjustment | Accumulated other comprehensive income (loss) | Accounting Standards Update 2016-01 |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in AOCI | $ 19 |  |  | $ 19 |  |  |  |  |  |
Cumulative Effect, Period of Adoption, Adjustment | Retained earnings |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in AOCI |  | 19 |  |  |  |  |  |  |  |
Cumulative Effect, Period of Adoption, Adjustment | Retained earnings | Accounting Standards Update 2016-01 |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Decrease in AOCI |  | 19 |  |  |  |  |  |  |  |
Revision of Prior Period, Error Correction, Adjustment | Underaccrued Payroll Tax Credits |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Payroll support and voluntary Employee programs, net |  | 88 |  |  |  |  |  |  |  |
Revision of Prior Period, Error Correction, Adjustment | Investment Gains |  |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |  |
Other (gains) losses, net |  | $ 60 |  |  |  |  |  |  |  |

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