Other Comprehensive Income and Accumulated Other Comprehensive Income (details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	$ 810	$ 2,236	$ 2,005
Other comprehensive income (loss) before reclassifications	52	(1,463)	217
Amounts reclassified from accumulated other comprehensive income	18	37	14
Other comprehensive income (loss), net of taxes	70	(1,426)	231
Balance, end of year	880	810	2,236
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	976	(2,734)	281
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	2	3	81
Net changes in benefit plan assets and obligations	(494)	647	(69)
Net changes in unrealized foreign currency translation	(289)	(112)	43
Other comprehensive income (loss) before income taxes	195	(2,196)	336
Income tax expense (benefit), other comprehensive income (loss)	125	(770)	105
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	1,125	2,908	2,729
Other comprehensive income (loss) before reclassifications	667	(1,740)	228
Amounts reclassified from accumulated other comprehensive income	(24)	(43)	(49)
Other comprehensive income (loss), net of taxes	643	(1,783)	179
Balance, end of year	1,768	1,125	2,908
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	976	(2,734)	281
Income tax expense (benefit), other comprehensive income (loss)	333	(951)	102
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	197	195	142
Other comprehensive income (loss) before reclassifications	(2)	(2)	48
Amounts reclassified from accumulated other comprehensive income	3	4	5
Other comprehensive income (loss), net of taxes	1	2	53
Balance, end of year	198	197	195
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	2	3	81
Income tax expense (benefit), other comprehensive income (loss)	1	1	28
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(431)	(857)	(811)
Other comprehensive income (loss) before reclassifications	(363)	358	(104)
Amounts reclassified from accumulated other comprehensive income	39	68	58
Other comprehensive income (loss), net of taxes	(324)	426	(46)
Balance, end of year	(755)	(431)	(857)
Net changes in benefit plan assets and obligations	(494)	647	(69)
Income tax expense (benefit), other comprehensive income (loss)	(170)	221	(23)
Net Unrealized Foreign Currency Translation [Member]
Accumulated other comprehensive income [Roll Forward]
Balance, beginning of year	(81)	(10)	(55)
Other comprehensive income (loss) before reclassifications	(250)	(79)	45
Amounts reclassified from accumulated other comprehensive income		8
Other comprehensive income (loss), net of taxes	(250)	(71)	45
Balance, end of year	(331)	(81)	(10)
Net changes in unrealized foreign currency translation	(289)	(112)	43
Income tax expense (benefit), other comprehensive income (loss)	$ (39)	$ (41)	$ (2)