Other Comprehensive Income and Accumulated Other Comprehensive Income (details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year			$ 880	$ 810
Other comprehensive income (loss) before reclassifications			(859)
Amounts reclassified from accumulated other comprehensive income			11
Other comprehensive income (loss), net of taxes	$ (137)	$ (262)	(848)	490
Balance, end of period	32	1,300	32	1,300
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	67	(154)	(829)	901
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	(3)	1	(13)	4
Net changes in benefit plan assets and obligations	24	15	71	45
Net changes in unrealized foreign currency translation	(227)	(203)	(407)	(149)
Other comprehensive income (loss) before income taxes	(139)	(341)	(1,178)	801
Income tax expense (benefit), other comprehensive income (loss)	(2)	(79)	(330)	311
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			(507)
Amounts reclassified from accumulated other comprehensive income			(36)
Other comprehensive income (loss), net of taxes	41	(99)	(543)	590
Balance, end of period	1,225		1,225
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	67	(154)	(829)	901
Income tax expense (benefit), other comprehensive income (loss)	26	(55)	(286)	311
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			(11)
Amounts reclassified from accumulated other comprehensive income			2
Other comprehensive income (loss), net of taxes	(3)		(9)	2
Balance, end of period	189		189
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	(3)	1	(13)	4
Income tax expense (benefit), other comprehensive income (loss)		1	(4)	2
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			45
Other comprehensive income (loss), net of taxes	15	10	46	28
Balance, end of period	(709)		(709)
Net changes in benefit plan assets and obligations	24	15	71	45
Income tax expense (benefit), other comprehensive income (loss)	9	5	25	17
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year			(331)
Other comprehensive income (loss) before reclassifications			(342)
Other comprehensive income (loss), net of taxes	(190)	(173)	(342)	(130)
Balance, end of period	(673)		(673)
Net changes in unrealized foreign currency translation	(227)	(203)	(407)	(149)
Income tax expense (benefit), other comprehensive income (loss)	$ (37)	$ (30)	$ (65)	$ (19)