Investment Securities (Investment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012 Debt Securities [Member]	Dec. 31, 2011 Debt Securities [Member]	Mar. 31, 2013 Domestic Corporate Debt Securities [Member]	Dec. 31, 2012 Domestic Corporate Debt Securities [Member]	Mar. 31, 2013 US States and Political Subdivisions Debt Securities [Member]	Dec. 31, 2012 US States and Political Subdivisions Debt Securities [Member]	Mar. 31, 2013 Residential Mortgage Backed Securities [Member]	Dec. 31, 2012 Residential Mortgage Backed Securities [Member]	Mar. 31, 2013 Commercial Mortgage Backed Securities [Member]	Dec. 31, 2012 Commercial Mortgage Backed Securities [Member]	Mar. 31, 2013 Asset-backed Securities [Member]	Dec. 31, 2012 Asset-backed Securities [Member]	Mar. 31, 2013 Foreign Corporate Debt Securities [Member]	Dec. 31, 2012 Foreign Corporate Debt Securities [Member]	Mar. 31, 2013 Foreign Government Debt Securities [Member]	Dec. 31, 2012 Foreign Government Debt Securities [Member]	Mar. 31, 2013 US Treasury and Government [Member]	Dec. 31, 2012 US Treasury and Government [Member]	Mar. 31, 2013 Retained Interest [Member]	Dec. 31, 2012 Retained Interest [Member]	Mar. 31, 2013 Available-for-sale Securities [Member]	Dec. 31, 2012 Available-for-sale Securities [Member]	Mar. 31, 2013 Trading Securities [Member]	Dec. 31, 2012 Trading Securities [Member]	Mar. 31, 2013 Total [Member]	Dec. 31, 2012 Total [Member]
Investment [Line Items]
Investment securities amortized cost					$ 20,098	$ 20,233	$ 4,207	$ 4,084	$ 2,123	$ 2,198	$ 2,941	$ 2,930	$ 5,621	$ 5,784	$ 2,409	$ 2,391	$ 1,904	$ 1,617	$ 3,404	$ 3,462	$ 74	$ 76	$ 404	$ 513	$ 186	$ 245	$ 43,371	$ 43,533
Investment securities gross unrealized gains					3,889	4,201	553	575	184	183	263	259	36	31	155	150	131	149	86	103	17	7	122	86	0	0	5,436	5,744
Investment securities gross unrealized loss					(88)	(302)	(112)	(113)	(90)	(119)	(78)	(95)	(55)	(77)	(110)	(126)	(3)	(3)	0	0	0	0	(10)	(3)	0	0	(546)	(838)
Investment securities estimated fair value					23,899	24,132	4,648	4,546	2,217	2,262	3,126	3,094	5,602	5,738	2,454	2,415	2,032	1,763	3,490	3,565	91	83	516	596	186	245	48,261	48,439
Net pre-tax gains (loss) on trading securities	36	(23)
Marketable securities OTTI amounts	289	32
Cumulative impairments recognized in earnings associated with debt securities			420	558
Marketable securities OTTI recorded in AOCI	11	0
Marketable Securities, Realized Loss, Other than Temporary Impairments, Amount	278	32
Incremental Charges On Previously Impaired Investment Securities	12	5
Other Than Temporary Impairment Related To Equity Securities	1	7
Other Than Temporary First Time Impairments Of Investment Securities Recognized In Earnings	263	7
Other Than Temporary Impairment Related To Securities Subsequently Sold	1	136
Proceeds from Sale of Available-for-sale Securities	2,788	3,762
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	$ 278