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)