Preferred Stock (Details) (USD $) In Millions, except Share data, unless otherwise specified					0 Months Ended			2 Months Ended	12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Preferred Stock [Member]	Dec. 31, 2011 Preferred Stock [Member]	Aug. 20, 2010 Cumulative Preferred Stock, Series E [Member]	Aug. 20, 2010 Cumulative Preferred Stock Series, F [Member]	Aug. 20, 2010 Cumulative Preferred Stock, Series G [Member]	Jun. 30, 2018 Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series I [Member]	Dec. 31, 2012 Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series I [Member]	Dec. 31, 2011 Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series I [Member]	Dec. 31, 2012 Non-Cumulative Preferred Stock, Series J [Member]	Dec. 31, 2011 Non-Cumulative Preferred Stock, Series J [Member]	Dec. 31, 2012 Non-Cumulative Preferred Stock, Series O [Member]	Dec. 31, 2011 Non-Cumulative Preferred Stock, Series O [Member]	Dec. 31, 2012 Earliest date Fixed-to-Floating Rate Non-Cumulative Perpetual Preferred Stock, Series I [Member]	Dec. 31, 2012 Earliest date Non-Cumulative Preferred Stock, Series J [Member]	Dec. 31, 2012 Earliest date Non-Cumulative Preferred Stock, Series O [Member]
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Shares of preferred stock authorized to issue, in one or more series	200,000,000	200,000,000	200,000,000
Preferred stock, par value per share	$ 1.00	$ 1.00	$ 1.00
Preferred stock dividend rate					6.15%	5.72%	5.49%		7.90%		8.625%		5.50%
Preferred stock dividend rate, variable								three-month LIBOR plus 3.47%
Preferred stock dividend rate, variable, description of basis									three-month LIBOR
Preferred stock dividend rate, variable, basis spread									3.47%
Shares	905,750	780,000	905,750	780,000					600,000	600,000	180,000	180,000	125,750	0
Carrying value (in millions)	$ 9,058	$ 7,800	$ 9,058	$ 7,800					$ 6,000	$ 6,000	$ 1,800	$ 1,800	$ 1,258	$ 0
Earliest redemption date															Apr. 30, 2018	Sep. 01, 2013	Sep. 01, 2017
Share value and redemption price per share									$ 10,000		$ 10,000		$ 10,000