Other Comprehensive Income and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period			$ 29,201
Other comprehensive income (loss), net of taxes	$ 478	$ 1,931	(733)	$ 1,242
Balance, end of period	29,156	26,943	29,156	26,943
Pre-tax components of other comprehensive loss and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	599	2,435	(946)	1,609
Income tax expense (benefit)	121	504	(213)	367
Other comprehensive income (loss), net of taxes	478	1,931	(733)	1,242
Accumulated Other Comprehensive Income [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period	1,291	(49)	2,502	640
Other comprehensive income (loss) before reclassifications	477		(743)
Amounts reclassified from accumulated other comprehensive income, net of tax	1		10
Other comprehensive income (loss), net of taxes	478	1,931	(733)	1,242
Balance, end of period	1,769	1,882	1,769	1,882
Pre-tax components of other comprehensive loss and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	599	2,435	(946)	1,609
Income tax expense (benefit)	121	504	(213)	367
Other comprehensive income (loss), net of taxes	478	1,931	(733)	1,242
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	2,635		3,892
Other comprehensive income (loss) before reclassifications	441		(805)
Amounts reclassified from accumulated other comprehensive income, net of tax	(19)		(30)
Other comprehensive income (loss), net of taxes	422	1,859	(835)	1,402
Balance, end of period	3,057		3,057
Pre-tax components of other comprehensive loss and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	533	2,359	(1,063)	1,784
Income tax expense (benefit)	111	500	(228)	382
Other comprehensive income (loss), net of taxes	422	1,859	(835)	1,402
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	2	0	(2)
Balance, end of period	182		182
Pre-tax components of other comprehensive loss and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	0	3	0	(3)
Income tax expense (benefit)	0	1	0	(1)
Other comprehensive income (loss), net of taxes	0	2	0	(2)
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period	(812)		(832)
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from accumulated other comprehensive income, net of tax	20		40
Other comprehensive income (loss), net of taxes	20	17	40	35
Balance, end of period	(792)		(792)
Pre-tax components of other comprehensive loss and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	26	21	51	44
Income tax expense (benefit)	6	4	11	9
Other comprehensive income (loss), net of taxes	20	17	40	35
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of period	(714)		(740)
Other comprehensive income (loss) before reclassifications	36		62
Amounts reclassified from accumulated other comprehensive income, net of tax	0		0
Other comprehensive income (loss), net of taxes	36	53	62	(193)
Balance, end of period	(678)		(678)
Pre-tax components of other comprehensive loss and the related income tax expense (benefit)
Other comprehensive income (loss), before taxes	40	52	66	(216)
Income tax expense (benefit)	4	(1)	4	(23)
Other comprehensive income (loss), net of taxes	$ 36	$ 53	$ 62	$ (193)