Other Comprehensive Income and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year			$ 25,943
Other comprehensive income, net of taxes	$ 256	$ 419	1,498	$ 2,484
Balance, end of period	27,849	25,607	27,849	25,607
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	309	541	1,918	3,147
Income tax expense (benefit)	53	122	420	663
Other comprehensive income, net of taxes	256	419	1,498	2,484
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	1,882	206	640	(1,859)
Other comprehensive income (loss) before reclassifications	258		1,472
Amounts reclassified from accumulated other comprehensive income	(2)		26
Other comprehensive income, net of taxes	256	419	1,498	2,484
Balance, end of period	2,138	625	2,138	625
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	309	541	1,918	3,147
Income tax expense (benefit)	53	122	420	663
Other comprehensive income, net of taxes	256	419	1,498	2,484
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 year	3,459		2,057
Other comprehensive income (loss) before reclassifications	189		1,597
Amounts reclassified from accumulated other comprehensive income	(18)		(24)
Other comprehensive income, net of taxes	171	478	1,573	2,468
Balance, end of period	3,630		3,630
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	217	605	2,001	3,129
Income tax expense (benefit)	46	127	428	661
Other comprehensive income, net of taxes	171	478	1,573	2,468
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 year	187		189
Other comprehensive income (loss) before reclassifications	(5)		(7)
Amounts reclassified from accumulated other comprehensive income	0		0
Other comprehensive income, net of taxes	(5)	(2)	(7)	(1)
Balance, end of period	182		182
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	(7)	(3)	(10)	(2)
Income tax expense (benefit)	(2)	(1)	(3)	(1)
Other comprehensive income, net of taxes	(5)	(2)	(7)	(1)
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(811)		(846)
Other comprehensive income (loss) before reclassifications	0		1
Amounts reclassified from accumulated other comprehensive income	16		50
Other comprehensive income, net of taxes	16	11	51	32
Balance, end of period	(795)		(795)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	20	14	64	40
Income tax expense (benefit)	4	3	13	8
Other comprehensive income, net of taxes	16	11	51	32
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(953)		(760)
Other comprehensive income (loss) before reclassifications	74		(119)
Amounts reclassified from accumulated other comprehensive income	0		0
Other comprehensive income, net of taxes	74	(68)	(119)	(15)
Balance, end of period	(879)		(879)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	79	(75)	(137)	(20)
Income tax expense (benefit)	5	(7)	(18)	(5)
Other comprehensive income, net of taxes	$ 74	$ (68)	$ (119)	$ (15)