Other Comprehensive Income and Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	$ 23,731	$ 23,731	$ 23,221
Other comprehensive income (loss), net of taxes		(1,470)	412	$ (598)
Balance, end of year		22,894	23,731	23,221
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		(1,819)	522	(887)
Income tax expense (benefit)		(349)	110	(289)
Other comprehensive income (loss), net of taxes		(1,470)	412	(598)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(343)	(343)	(755)	(157)
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		(1,513)	518	(605)
Amounts reclassified from accumulated other comprehensive income		43	(106)	7
Other comprehensive income (loss), net of taxes		(1,470)	412	(598)
Balance, end of year		(1,859)	(343)	(755)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		(1,819)	522	(887)
Income tax expense (benefit)		(349)	110	(289)
Other comprehensive income (loss), net of taxes		(1,470)	412	(598)
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	747	747	528	1,100
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		(1,151)	367	(530)
Amounts reclassified from accumulated other comprehensive income		(25)	(148)	(42)
Other comprehensive income (loss), net of taxes		(1,176)	219	(572)
Balance, end of year		(306)	747	528
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		(1,489)	294	(883)
Income tax expense (benefit)		(313)	75	(311)
Other comprehensive income (loss), net of taxes		(1,176)	219	(572)
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	207	207	202	189
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		(21)	4	4
Amounts reclassified from accumulated other comprehensive income			1	9
Other comprehensive income (loss), net of taxes		(21)	5	13
Balance, end of year		193	207	202
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		(27)	8	21
Income tax expense (benefit)		(6)	3	8
Other comprehensive income (loss), net of taxes		(21)	5	13
Net Benefit Plan Assets and Obligations Recognized in Shareholders’ Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(686)	(686)	(703)	(713)
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		(114)	(24)	(30)
Amounts reclassified from accumulated other comprehensive income		68	41	40
Other comprehensive income (loss), net of taxes		(46)	17	10
Balance, end of year		(873)	(686)	(703)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		(56)	29	16
Income tax expense (benefit)		(10)	12	6
Other comprehensive income (loss), net of taxes		(46)	17	10
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(611)	(611)	(782)	(733)
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		(227)	171	(49)
Other comprehensive income (loss), net of taxes		(227)	171	(49)
Balance, end of year		(873)	(611)	(782)
Pre-tax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes		(247)	191	(41)
Income tax expense (benefit)		(20)	20	8
Other comprehensive income (loss), net of taxes		$ (227)	$ 171	$ (49)