Variable Interest Entities - Loans Sold to Third-Party Sponsored Securitization Entities (Details) (Variable Interest Entity, Not Primary Beneficiary, USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Variable Interest Entity, Not Primary Beneficiary
Summary of loan sale activities [Abstract]
Carrying value of loans sold	$ 12,139,000,000	$ 13,920,000,000
Proceeds received from loan sales as cash	51,000,000	39,000,000
Proceeds received from loan sales as securities	12,029,000,000	13,735,000,000
Total proceeds received from loan sales	12,080,000,000	13,774,000,000
Gains on loan sales	91,000,000	37,000,000
Loans repurchased	12,300,000,000		12,400,000,000
Real estate acquired through foreclosure	$ 471,000,000		$ 464,000,000