Other Comprehensive Income and Accumulated Other Comprehensive Income (details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated other comprehensive income [Roll Forward]
Shareholders' equity, beginning of year			$ 23,598
Other comprehensive income (loss), net of taxes	$ 551	$ (600)	1,122	$ (711)
Shareholders' equity, end of period	24,714	24,121	24,714	24,121
Pretax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes	874	(953)	1,712	(1,039)
Income tax expense (benefit), other comprehensive income (loss)	323	(353)	590	(328)
Other comprehensive income (loss), net of taxes	551	(600)	1,122	(711)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated other comprehensive income [Roll Forward]
Shareholders' equity, beginning of year			(157)	880
Other comprehensive income before reclassifications			1,117
Amounts reclassified from accumulated other comprehensive income			5
Other comprehensive income (loss), net of taxes	551	(600)	1,122	(711)
Shareholders' equity, end of period	965	169	965	169
Pretax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes	874	(953)	1,712	(1,039)
Income tax expense (benefit), other comprehensive income (loss)	323	(353)	590	(328)
Other comprehensive income (loss), net of taxes	551	(600)	1,122	(711)
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]
Shareholders' equity, beginning of year			1,100
Other comprehensive income before reclassifications			1,064
Amounts reclassified from accumulated other comprehensive income			(23)
Other comprehensive income (loss), net of taxes	574	(697)	1,041	(584)
Shareholders' equity, end of period	2,141		2,141
Pretax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes	879	(1,065)	1,593	(896)
Income tax expense (benefit), other comprehensive income (loss)	305	(368)	552	(312)
Other comprehensive income (loss), net of taxes	574	(697)	1,041	(584)
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]
Shareholders' equity, beginning of year			189
Other comprehensive income before reclassifications			3
Amounts reclassified from accumulated other comprehensive income			8
Other comprehensive income (loss), net of taxes	8	(3)	11	(6)
Shareholders' equity, end of period	200		200
Pretax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes	12	(5)	17	(10)
Income tax expense (benefit), other comprehensive income (loss)	4	(2)	6	(4)
Other comprehensive income (loss), net of taxes	8	(3)	11	(6)
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Shareholders' equity, beginning of year			(713)
Other comprehensive income before reclassifications			3
Amounts reclassified from accumulated other comprehensive income			20
Other comprehensive income (loss), net of taxes	12	15	23	31
Shareholders' equity, end of period	(690)		(690)
Pretax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes	18	23	34	47
Income tax expense (benefit), other comprehensive income (loss)	6	8	11	16
Other comprehensive income (loss), net of taxes	12	15	23	31
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Shareholders' equity, beginning of year			(733)
Other comprehensive income before reclassifications			47
Other comprehensive income (loss), net of taxes	(43)	85	47	(152)
Shareholders' equity, end of period	(686)		(686)
Pretax components of other comprehensive income (loss) and related tax expense (benefit)
Other comprehensive income (loss) before income taxes	(35)	94	68	(180)
Income tax expense (benefit), other comprehensive income (loss)	8	9	21	(28)
Other comprehensive income (loss), net of taxes	$ (43)	$ 85	$ 47	$ (152)