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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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