Other Comprehensive Income and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year			$ 25,943
Other comprehensive income, net of taxes	$ 1,931	$ 888	1,242	$ 2,065
Balance, end of period	26,943	25,321	26,943	25,321
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	2,435	1,123	1,609	2,606
Income tax expense (benefit)	504	235	367	541
Other comprehensive income, net of taxes	1,931	888	1,242	2,065
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(49)	(682)	640	(1,859)
Other comprehensive income (loss) before reclassifications	1,922		1,214
Amounts reclassified from accumulated other comprehensive income	9		28
Other comprehensive income, net of taxes	1,931	888	1,242	2,065
Balance, end of period	1,882	206	1,882	206
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	2,435	1,123	1,609	2,606
Income tax expense (benefit)	504	235	367	541
Other comprehensive income, net of taxes	1,931	888	1,242	2,065
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	1,600		2,057
Other comprehensive income (loss) before reclassifications	1,867		1,408
Amounts reclassified from accumulated other comprehensive income	(8)		(6)
Other comprehensive income, net of taxes	1,859	874	1,402	1,990
Balance, end of period	3,459		3,459
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	2,359	1,108	1,784	2,524
Income tax expense (benefit)	500	234	382	534
Other comprehensive income, net of taxes	1,859	874	1,402	1,990
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	185		189
Other comprehensive income (loss) before reclassifications	2		(2)
Amounts reclassified from accumulated other comprehensive income	0		0
Other comprehensive income, net of taxes	2	(3)	(2)	1
Balance, end of period	187		187
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	3	(4)	(3)	1
Income tax expense (benefit)	1	(1)	(1)	0
Other comprehensive income, net of taxes	2	(3)	(2)	1
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(828)		(846)
Other comprehensive income (loss) before reclassifications	0		1
Amounts reclassified from accumulated other comprehensive income	17		34
Other comprehensive income, net of taxes	17	11	35	21
Balance, end of period	(811)		(811)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	21	14	44	26
Income tax expense (benefit)	4	3	9	5
Other comprehensive income, net of taxes	17	11	35	21
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(1,006)		(760)
Other comprehensive income (loss) before reclassifications	53		(193)
Amounts reclassified from accumulated other comprehensive income	0		0
Other comprehensive income, net of taxes	53	6	(193)	53
Balance, end of period	(953)		(953)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income before income taxes	52	5	(216)	55
Income tax expense (benefit)	(1)	(1)	(23)	2
Other comprehensive income, net of taxes	$ 53	$ 6	$ (193)	$ 53