Variable Interest Entities - Loans Sold to Third-Party Sponsored Securitization Entities (Details 5) (Variable Interest Entity, Not Primary Beneficiary, USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Variable Interest Entity, Not Primary Beneficiary
Summary of loan sale activities [Abstract]
Carrying value of loans sold	$ 54,880,000,000	$ 39,808,000,000
Proceeds from Sale of Mortgage Loans Held-for-sale	166,000,000	18,000,000
Proceeds received from loan sales as securities	54,169,000,000	39,255,000,000
Total proceeds received from loan sales	54,335,000,000	39,273,000,000
Gains on loan sales	138,000,000	35,000,000
Loans Repurchased Or Loans With The Option To Repurchase	15,600,000,000		15,600,000,000
Real Estate Acquired Through Foreclosure	$ 1,700,000,000		$ 1,600,000,000