Other Comprehensive Income and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	$ 29,201	$ 25,943
Other comprehensive income (loss), net of taxes	(1,309)	1,862	$ 2,499
Balance, end of year	28,887	29,201	25,943
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before income taxes	(1,671)	2,352	3,140
Income tax expense (benefit)	(362)	490	641
Other comprehensive income (loss), net of taxes	(1,309)	1,862	2,499
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	2,502	640	(1,859)
Other comprehensive income (loss) before reclassifications	(1,337)	1,837	2,494
Amounts reclassified from accumulated other comprehensive income, net of tax	28	25	5
Other comprehensive income (loss), net of taxes	(1,309)	1,862	2,499
Balance, end of year	1,193	2,502	640
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before income taxes	(1,671)	2,352	3,140
Income tax expense (benefit)	(362)	490	641
Other comprehensive income (loss), net of taxes	(1,309)	1,862	2,499
Changes in Net Unrealized Gains (Losses) on Investment Securities Having No Credit Losses Recognized in the Consolidated Statement of Income [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	3,892	2,057	(306)
Other comprehensive income (loss) before reclassifications	(1,606)	1,876	2,406
Amounts reclassified from accumulated other comprehensive income, net of tax	(53)	(41)	(43)
Other comprehensive income (loss), net of taxes	(1,659)	1,835	2,363
Balance, end of year	2,233	3,892	2,057
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before income taxes	(2,115)	2,331	2,994
Income tax expense (benefit)	(456)	496	631
Other comprehensive income (loss), net of taxes	(1,659)	1,835	2,363
Changes in Net Unrealized Gains (Losses) on Investment Securities Having Credit Losses Recognized in the Consolidated Statement of Income [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	182	189	193
Other comprehensive income (loss) before reclassifications	0	(7)	(4)
Amounts reclassified from accumulated other comprehensive income, net of tax	0	0	0
Other comprehensive income (loss), net of taxes	0	(7)	(4)
Balance, end of year	182	182	189
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before income taxes	0	(9)	(4)
Income tax expense (benefit)	0	(2)	0
Other comprehensive income (loss), net of taxes	0	(7)	(4)
Net Benefit Plan Assets and Obligations Recognized in Shareholders’ Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(832)	(846)	(873)
Other comprehensive income (loss) before reclassifications	278	(53)	(14)
Amounts reclassified from accumulated other comprehensive income, net of tax	81	67	41
Other comprehensive income (loss), net of taxes	359	14	27
Balance, end of year	(473)	(832)	(846)
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before income taxes	455	18	33
Income tax expense (benefit)	96	4	6
Other comprehensive income (loss), net of taxes	359	14	27
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(740)	(760)	(873)
Other comprehensive income (loss) before reclassifications	(9)	21	106
Amounts reclassified from accumulated other comprehensive income, net of tax	0	(1)	7
Other comprehensive income (loss), net of taxes	(9)	20	113
Balance, end of year	(749)	(740)	(760)
Pre-tax components of other comprehensive income (loss) and the related income tax expense (benefit)
Other comprehensive income (loss), before income taxes	(11)	12	117
Income tax expense (benefit)	(2)	(8)	4
Other comprehensive income (loss), net of taxes	$ (9)	$ 20	$ 113