Shareholders' Equity (Narrative) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
	Apr. 30, 2012	Mar. 31, 2011	Jun. 30, 2012	Dec. 31, 2011	Dec. 31, 2010
Shareholders' Equity [Line Items]
Stock Repurchase Program, Authorized Amount			$ 1,800,000,000
Common stock acquired, shares			11.1
Stock Repurchased During Period, Average Price Per Share			$ 43.26
Common Stock Approximate Aggregate Cost	480,000,000
Realized (losses) gains from sales of investment securities		66,000,000	5,000,000
Unrealized pre-tax gains (losses) included in other comprehensive income				17,000,000	76,000,000
Deferred taxes related to unrealized pre-tax gains				$ 7,000,000	$ 30,000,000