Other Comprehensive Income and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	$ 23,731	$ 22,894	$ 23,731
Other comprehensive income (loss), net of taxes		2,499	(1,470)	$ 412
Balance, end of year		25,943	22,894	23,731
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		3,140	(1,819)	522
Income tax expense (benefit)		641	(349)	110
Other comprehensive income (loss), net of taxes		2,499	(1,470)	412
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(343)	(1,859)	(343)	(755)
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, pre-tax	(34)
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, tax	(12)
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, net of income taxes	(22)			(22)
Reclassification of certain tax effects from adoption of updated accounting guidance	(24)		(24)
Effect of adoption of updated accounting guidance, net of tax, total	(46)
Other comprehensive income (loss) before reclassifications		2,494	(1,513)	518
Amounts reclassified from accumulated other comprehensive income		5	43	(106)
Other comprehensive income (loss), net of taxes		2,499	(1,470)	412
Balance, end of year		640	(1,859)	(343)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		3,140	(1,819)	522
Income tax expense (benefit)		641	(349)	110
Other comprehensive income (loss), net of taxes		2,499	(1,470)	412
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	747	(306)	747	528
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, pre-tax	(34)
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, tax	(12)
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, net of income taxes	(22)
Reclassification of certain tax effects from adoption of updated accounting guidance	145
Effect of adoption of updated accounting guidance, net of tax, total	123
Other comprehensive income (loss) before reclassifications		2,406	(1,151)	367
Amounts reclassified from accumulated other comprehensive income		(43)	(25)	(148)
Other comprehensive income (loss), net of taxes		2,363	(1,176)	219
Balance, end of year		2,057	(306)	747
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		2,994	(1,489)	294
Income tax expense (benefit)		631	(313)	75
Other comprehensive income (loss), net of taxes		2,363	(1,176)	219
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	207	193	207	202
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, pre-tax	0
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, tax	0
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, net of income taxes	0
Reclassification of certain tax effects from adoption of updated accounting guidance	7
Effect of adoption of updated accounting guidance, net of tax, total	7
Other comprehensive income (loss) before reclassifications		(4)	(21)	4
Amounts reclassified from accumulated other comprehensive income		0	0	1
Other comprehensive income (loss), net of taxes		(4)	(21)	5
Balance, end of year		189	193	207
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		(4)	(27)	8
Income tax expense (benefit)		0	(6)	3
Other comprehensive income (loss), net of taxes		(4)	(21)	5
Net Benefit Plan Assets and Obligations Recognized in Shareholders’ Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(686)	(873)	(686)	(703)
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, pre-tax	0
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, tax	0
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, net of income taxes	0
Reclassification of certain tax effects from adoption of updated accounting guidance	(141)
Effect of adoption of updated accounting guidance, net of tax, total	(141)
Other comprehensive income (loss) before reclassifications		(14)	(114)	(24)
Amounts reclassified from accumulated other comprehensive income		41	68	41
Other comprehensive income (loss), net of taxes		27	(46)	17
Balance, end of year		(846)	(873)	(686)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		33	(56)	29
Income tax expense (benefit)		6	(10)	12
Other comprehensive income (loss), net of taxes		27	(46)	17
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(611)	(873)	(611)	(782)
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, pre-tax	0
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, tax	0
Cumulative effect of adoption of updated accounting guidance for equity financial instruments, net of income taxes	0
Reclassification of certain tax effects from adoption of updated accounting guidance	(35)
Effect of adoption of updated accounting guidance, net of tax, total	$ (35)
Other comprehensive income (loss) before reclassifications		106	(227)	171
Amounts reclassified from accumulated other comprehensive income		7	0	0
Other comprehensive income (loss), net of taxes		113	(227)	171
Balance, end of year		(760)	(873)	(611)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		117	(247)	191
Income tax expense (benefit)		4	(20)	20
Other comprehensive income (loss), net of taxes		$ 113	$ (227)	$ 171