Other Comprehensive Income and Accumulated Other Comprehensive Income (details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year			$ 880	$ 810
Other comprehensive income (loss) before reclassifications			(720)
Amounts reclassified from accumulated other comprehensive income			9
Other comprehensive income (loss), net of taxes	$ (600)	$ 435	(711)	752
Balance, end of period	169	1,562	169	1,562
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	(1,065)	518	(896)	1,055
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	(5)	1	(10)	3
Net changes in benefit plan assets and obligations	23	15	47	30
Net changes in unrealized foreign currency translation	94	97	(180)	54
Other comprehensive income (loss) before income taxes	(953)	631	(1,039)	1,142
Income tax expense (benefit), other comprehensive income (loss)	(353)	196	(328)	390
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			1,768
Other comprehensive income (loss) before reclassifications			(561)
Amounts reclassified from accumulated other comprehensive income			(23)
Other comprehensive income (loss), net of taxes	(697)	338	(584)	689
Balance, end of period	1,184		1,184
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	(1,065)	518	(896)	1,055
Income tax expense (benefit), other comprehensive income (loss)	(368)	180	(312)	366
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			198
Other comprehensive income (loss) before reclassifications			(8)
Amounts reclassified from accumulated other comprehensive income			2
Other comprehensive income (loss), net of taxes	(3)	1	(6)	2
Balance, end of period	192		192
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	(5)	1	(10)	3
Income tax expense (benefit), other comprehensive income (loss)	(2)		(4)	1
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year			(755)
Other comprehensive income (loss) before reclassifications			1
Amounts reclassified from accumulated other comprehensive income			30
Other comprehensive income (loss), net of taxes	15	10	31	18
Balance, end of period	(724)		(724)
Net changes in benefit plan assets and obligations	23	15	47	30
Income tax expense (benefit), other comprehensive income (loss)	8	5	16	12
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year			(331)
Other comprehensive income (loss) before reclassifications			(152)
Other comprehensive income (loss), net of taxes	85	86	(152)	43
Balance, end of period	(483)		(483)
Net changes in unrealized foreign currency translation	94	97	(180)	54
Income tax expense (benefit), other comprehensive income (loss)	$ 9	$ 11	$ (28)	$ 11