Shareholders' Equity and Dividend Availability (details) - Accumulated Other Changes in Equity from Nonowner Sources (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Changes in each component of Accumulated Other Changes in Equity from Nonowner Sources [Roll Forward]
Accumulated other changes in equity from nonowner sources, net of tax, balance, beginning of year	$ 1,255	$ 1,219	$ (900)
Accumulated other changes in equity from nonowner sources, net of tax, cumulative effect of adoption of updated accounting guidance at April 1, 2009			(71)
Net change in unrealized gains on investment securities, net of tax	1,083	204	2,085
Reclassification adjustment for net realized gains included in net income, net of tax	(71)	(201)	(12)
Net change in benefit plan assets and obligations recognized in equity, net of tax	(201)	27	(88)
Accumulated other changes in equity from nonowner sources, change in other, net of tax	(61)	6	205
Accumulated other changes in equity from nonowner sources, net of tax, current period change	750	36	2,119
Accumulated other changes in equity from nonowner sources, net of tax, balance, end of year	2,005	1,255	1,219
Net Unrealized Gains (Losses) on Investment Securities [Member]
Changes in each component of Accumulated Other Changes in Equity from Nonowner Sources [Roll Forward]
Accumulated other changes in equity from nonowner sources, net of tax, balance, beginning of year	1,859	1,856	(146)
Accumulated other changes in equity from nonowner sources, net of tax, cumulative effect of adoption of updated accounting guidance at April 1, 2009			(71)
Accumulated other changes in equity from nonowner sources, cumulative effect of adoption of updated accounting guidance at April 1, 2009, tax expense (benefit)			(38)
Net change in unrealized gains on investment securities, net of tax	1,083	204	2,085
Net change in unrealized gains on investment securities, tax expense (benefit)	600	110	1,119
Reclassification adjustment for net realized gains included in net income, net of tax	(71)	(201)	(12)
Reclassification adjustment for net realized gains included in net income, tax expense (benefit)	(38)	(108)	(6)
Accumulated other changes in equity from nonowner sources, net of tax, current period change	1,012	3	2,002
Accumulated other changes in equity from nonowner sources, net of tax, balance, end of year	2,871	1,859	1,856
Net Benefit Plan Assets and Obligations Recognized in Equity [Member]
Changes in each component of Accumulated Other Changes in Equity from Nonowner Sources [Roll Forward]
Accumulated other changes in equity from nonowner sources, net of tax, balance, beginning of year	(610)	(637)	(549)
Net change in benefit plan assets and obligations recognized in equity, net of tax	(201)	27	(88)
Net change in benefit plan assets and obligations recognized in equity, tax expense (benefit)	(106)	12	(47)
Accumulated other changes in equity from nonowner sources, net of tax, current period change	(201)	27	(88)
Accumulated other changes in equity from nonowner sources, net of tax, balance, end of year	(811)	(610)	(637)
Net Unrealized Foreign Currency Translation and Other [Member]
Changes in each component of Accumulated Other Changes in Equity from Nonowner Sources [Roll Forward]
Accumulated other changes in equity from nonowner sources, net of tax, balance, beginning of year	6		(205)
Accumulated other changes in equity from nonowner sources, change in other, net of tax	(61)	6	205
Accumulated other changes in equity from nonowner sources, change in other, tax expense (benefit)	(29)	6	46
Accumulated other changes in equity from nonowner sources, net of tax, current period change	(61)	6	205
Accumulated other changes in equity from nonowner sources, net of tax, balance, end of year	$ (55)	$ 6