Shareholders' Equity (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended	3 Months Ended			9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 March 2013 Repurchase Program	Sep. 30, 2013 March 2013 Repurchase Program	Mar. 31, 2013 March 2013 Repurchase Program	Sep. 30, 2013 March 2013 Repurchase Program	Sep. 30, 2013 March 2013 Repurchase Program	Mar. 31, 2013 March 2012 Share Repurchase Program	Sep. 30, 2013 Retained Earnings	Sep. 30, 2012 Retained Earnings	Sep. 30, 2013 Retained Earnings	Sep. 30, 2012 Retained Earnings	Sep. 30, 2013 Series C Preferred Stock	Sep. 30, 2012 Series C Preferred Stock	Sep. 30, 2013 Series C Preferred Stock	Sep. 30, 2012 Series C Preferred Stock	Sep. 30, 2013 Depositary Shares	Sep. 30, 2013 Depositary Shares	Sep. 30, 2012 Series A Preferred Stock	Sep. 30, 2012 Series A Preferred Stock
Equity, Class of Treasury Stock [Line Items]
Amount of common stock authorized for repurchase							$ 2,100,000,000
Common stock acquired (shares)			23,200,000					8,200,000	0	16,700,000		6,500,000
Remaining authorized repurchase amount											980,000,000
Average cost per share of treasury shares repurchased (per share)			$ 63.69					$ 68.57		$ 67.12		$ 54.95
Approximate aggregate cost of treasury shares repurchased			1,480,000,000					560,000,000		1,120,000,000		360,000,000
Cash dividends declared (in dollars per share)	$ 0.26	$ 0.24	$ 0.78	$ 0.72
Common stock dividends			350,000,000	346,000,000									115,000,000	113,000,000	350,000,000	346,000,000
Depositary shares, ownership interest																	0.025%
Preferred stock dividends (in dollars per share)																	$ 1,312.50		$ 3,937.50		$ 0.33	$ 0.98
Dividends, Preferred Stock, Cash			20,000,000	29,000,000											20,000,000	29,000,000	7,000,000	8,000,000	20,000,000	8,000,000			7,000,000	21,000,000
Realized gains (losses) from sale of available-for-sale securities				29,000,000
Net gains (losses) from sales of available-for-sale securities			11,000,000
Unrealized pretax gains (losses) on securities included in AOCI					25,000,000	22,000,000
Deferred taxes on unrealized pretax gains (losses) on securities included in AOCI					$ 10,000,000	$ 9,000,000