Other Comprehensive Income and Accumulated Other Comprehensive Income (details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accumulated other comprehensive income [Roll Forward]
Accumulated other comprehensive income, net of tax, balance, beginning of year	$ 2,005	$ 1,255	$ 1,219
Other comprehensive income before reclassifications	217	771	197
Amounts reclassified from accumulated other comprehensive income	14	(21)	(161)
Net other comprehensive income, current period	231	750	36
Accumulated other comprehensive income, net of tax, balance, end of year	2,236	2,005	1,255
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	281	1,570	(118)
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	81	4	123
Net changes in benefit plan assets and obligations	(69)	(307)	39
Net changes in unrealized foreign currency translation and other changes	43	(90)	12
Other comprehensive income before income taxes	336	1,177	56
Income tax expense, other comprehensive income	105	427	20
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]
Accumulated other comprehensive income, net of tax, balance, beginning of year	2,729	1,719	1,796
Other comprehensive income before reclassifications	228	1,091	130
Amounts reclassified from accumulated other comprehensive income	(49)	(81)	(207)
Net other comprehensive income, current period	179	1,010	(77)
Accumulated other comprehensive income, net of tax, balance, end of year	2,908	2,729	1,719
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income	281	1,570	(118)
Income tax expense, other comprehensive income	102	560	(41)
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]
Accumulated other comprehensive income, net of tax, balance, beginning of year	142	140	60
Other comprehensive income before reclassifications	48	(8)	74
Amounts reclassified from accumulated other comprehensive income	5	10	6
Net other comprehensive income, current period	53	2	80
Accumulated other comprehensive income, net of tax, balance, end of year	195	142	140
Changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income	81	4	123
Income tax expense, other comprehensive income	28	2	43
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member]
Accumulated other comprehensive income [Roll Forward]
Accumulated other comprehensive income, net of tax, balance, beginning of year	(811)	(610)	(637)
Other comprehensive income before reclassifications	(104)	(251)	(13)
Amounts reclassified from accumulated other comprehensive income	58	50	40
Net other comprehensive income, current period	(46)	(201)	27
Accumulated other comprehensive income, net of tax, balance, end of year	(857)	(811)	(610)
Net changes in benefit plan assets and obligations	(69)	(307)	39
Income tax expense, other comprehensive income	(23)	(106)	12
Net Unrealized Foreign Currency Translation and Other [Member]
Accumulated other comprehensive income [Roll Forward]
Accumulated other comprehensive income, net of tax, balance, beginning of year	(55)	6
Other comprehensive income before reclassifications	45	(61)	6
Net other comprehensive income, current period	45	(61)	6
Accumulated other comprehensive income, net of tax, balance, end of year	(10)	(55)	6
Net changes in unrealized foreign currency translation and other changes	43	(90)	12
Income tax expense, other comprehensive income	$ (2)	$ (29)	$ 6