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Basis of Presentation (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2021 | Dec. 31, 2020 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Dec. 31, 2020 | Mar. 31, 2021 | Mar. 31, 2020 | Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |
Payroll support and voluntary Employee programs, net | $ 740 |  | $ 784 | $ 2,187 | $ 784 |  |  |  |
Other (gains) losses, net | (14) |  | 32 | (61) | 60 |  |  |  |
Decrease in AOCI | (9,688) | $ (8,876) | (10,878) | (9,688) | (10,878) | $ (8,876) | $ (9,093) | $ (9,075) | $ (9,832)
Accumulated other comprehensive income (loss) |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |
Decrease in AOCI | (136) | 105 | 130 | (136) | 130 | 105 | 60 | 186 | 61
Retained earnings |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |
Decrease in AOCI | $ (15,260) | (14,777) | $ (16,842) | $ (15,260) | $ (16,842) | (14,777) | $ (14,912) | $ (17,757) | $ (17,945)
Cumulative effect of adopting Accounting Standards Update No. 2016-01, Financial Instruments (See Note 1) |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |
Decrease in AOCI |  | 0 |  |  |  | 0 |  |  |
Cumulative effect of adopting Accounting Standards Update No. 2016-01, Financial Instruments (See Note 1) | Accumulated other comprehensive income (loss) |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |
Decrease in AOCI |  | 19 |  |  |  | 19 |  |  |
Cumulative effect of adopting Accounting Standards Update No. 2016-01, Financial Instruments (See Note 1) | Retained earnings |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |
Decrease in AOCI |  | (19) |  |  |  | (19) |  |  |
Cumulative effect of adopting Accounting Standards Update No. 2016-01, Financial Instruments (See Note 1) | Accounting Standards Update 2016-01 | Accumulated other comprehensive income (loss) |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |
Decrease in AOCI |  | 19 |  |  |  | 19 |  |  |
Cumulative effect of adopting Accounting Standards Update No. 2016-01, Financial Instruments (See Note 1) | Accounting Standards Update 2016-01 | Retained earnings |  |  |  |  |  |  |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |  |  |  |  |  |  |
Decrease in AOCI |  | (19) |  |  |  | (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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