Shareholders' Equity (Narrative) (Details) (USD $)	1 Months Ended	3 Months Ended				9 Months Ended				12 Months Ended			3 Months Ended	9 Months Ended			0 Months Ended	9 Months Ended
	Mar. 30, 2012	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011	Dec. 31, 2010	Aug. 21, 2012	Sep. 30, 2012 Series C Preferred Stock [Member]	Sep. 30, 2012 Series C Preferred Stock [Member]	Aug. 21, 2012 Series C Preferred Stock [Member]	Dec. 31, 2011 Series C Preferred Stock [Member]	Oct. 04, 2012 Series A Preferred Stock [Member]	Sep. 30, 2012 Series A Preferred Stock [Member]	Sep. 04, 2012 Series A Preferred Stock [Member]	Dec. 31, 2011 Series A Preferred Stock [Member]
Shareholders' Equity [Line Items]
Depositary shares issued and sold												20,000,000
Depositary shares' ownership interest in series C preferred stock, on a per share basis															$ 0.00025
Preferred stock liquidation preference per share													$ 100,000	$ 100,000			$ 100,000		$ 100,000
Value of Preferred Stock Series A redeemed																	$ 500,000,000	$ 500,000,000
Depositary shares liquidation preference per share		$ 25				$ 25
Preferred stock annual dividend rate														5.25%
Preferred stock dividend declared		15,000,000	[1]	6,000,000	[1]	29,000,000	[1]	13,000,000	[1]				8,000,000	8,000,000
Preferred stock shares issued													5,000	5,000		5,000		5,001	5,001	5,001
Value of preferred stock issued													488,000,000	488,000,000		0		0		500,000,000
Preferred stock dividend unpaid amount																	7,000,000
Authorized repurchase amount under stock repurchase program	1,800,000,000
Average cost per share of treasury stock acquired		$ 42.11				$ 42.68
Common stock acquired		11,400,000				22,500,000
Approximate aggregate cost of common stock acquired		480,000,000				960,000,000
Realized (losses) gains from sales of investment securities						29,000,000		81,000,000
Unrealized pre-tax gains (losses) included in other comprehensive income										22,000,000	65,000,000
Deferred taxes related to unrealized pre-tax gains										$ 9,000,000	$ 26,000,000

[1] Three and nine months ended September 30, 2012 included $8 million related to Series C preferred stock issued in August 2012. Remaining amounts for 2012 periods, and amounts for three and nine months ended September 30, 2011, related to Series A preferred stock, which was redeemed on October 4, 2012.