Shareholders' Equity (Narrative) (Details) (USD $)	6 Months Ended		12 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended	3 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 March 2013 Repurchase Program [Member]	Jun. 30, 2013 March 2013 Repurchase Program [Member]	Mar. 31, 2013 March 2013 Repurchase Program [Member]	Jun. 30, 2013 March 2013 Repurchase Program [Member]	Mar. 31, 2013 March 2012 Share Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase					$ 2,100,000,000.0
Common stock acquired (shares)	15,000,000					8,500,000	0		6,500,000
Remaining authorized repurchase amount								1,540,000,000
Average cost per share of treasury shares repurchased (per share)	$ 61.04					$ 65.73			$ 54.95
Approximate aggregate cost of treasury shares repurchased	920,000,000					560,000,000			360,000,000
Realized gains (losses) from sale of available-for-sale securities	5,000,000	5,000,000
Unrealized pretax gains (losses) on securities included in AOCI			15,000,000	17,000,000
Deferred taxes on unrealized pretax gains (losses) on securities included in AOCI			$ 6,000,000	$ 7,000,000