Other Comprehensive Income and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period			$ 29,201
Other comprehensive income (loss), net of taxes	$ (603)	$ 256	(1,336)	$ 1,498
Balance, end of period	28,474	27,849	28,474	27,849
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	(751)	309	(1,697)	1,918
Income tax expense (benefit)	(148)	53	(361)	420
Other comprehensive income (loss), net of taxes	(603)	256	(1,336)	1,498
Accumulated Other Comprehensive Income [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period	1,769	1,882	2,502	640
Other comprehensive income (loss) before reclassifications	(614)		(1,357)
Amounts reclassified from accumulated other comprehensive income, net of tax	11		21
Other comprehensive income (loss), net of taxes	(603)	256	(1,336)	1,498
Balance, end of period	1,166	2,138	1,166	2,138
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	(751)	309	(1,697)	1,918
Income tax expense (benefit)	(148)	53	(361)	420
Other comprehensive income (loss), net of taxes	(603)	256	(1,336)	1,498
Changes in Net Unrealized Gains on Investment Securities Having No Credit Losses Recognized in the Consolidated Statement of Income [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period	3,057		3,892
Other comprehensive income (loss) before reclassifications	(530)		(1,335)
Amounts reclassified from accumulated other comprehensive income, net of tax	(10)		(40)
Other comprehensive income (loss), net of taxes	(540)	171	(1,375)	1,573
Balance, end of period	2,517		2,517
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	(686)	217	(1,749)	2,001
Income tax expense (benefit)	(146)	46	(374)	428
Other comprehensive income (loss), net of taxes	(540)	171	(1,375)	1,573
Changes in Net Unrealized Gains on Investment Securities Having Credit Losses Recognized in the Consolidated Statement of Income [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period	182		182
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from accumulated other comprehensive income, net of tax	0		0
Other comprehensive income (loss), net of taxes	0	(5)	0	(7)
Balance, end of period	182		182
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	0	(7)	0	(10)
Income tax expense (benefit)	0	(2)	0	(3)
Other comprehensive income (loss), net of taxes	0	(5)	0	(7)
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period	(792)		(832)
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from accumulated other comprehensive income, net of tax	21		61
Other comprehensive income (loss), net of taxes	21	16	61	51
Balance, end of period	(771)		(771)
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	26	20	77	64
Income tax expense (benefit)	5	4	16	13
Other comprehensive income (loss), net of taxes	21	16	61	51
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period	(678)		(740)
Other comprehensive income (loss) before reclassifications	(84)		(22)
Amounts reclassified from accumulated other comprehensive income, net of tax	0		0
Other comprehensive income (loss), net of taxes	(84)	74	(22)	(119)
Balance, end of period	(762)		(762)
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	(91)	79	(25)	(137)
Income tax expense (benefit)	(7)	5	(3)	(18)
Other comprehensive income (loss), net of taxes	$ (84)	$ 74	$ (22)	$ (119)