Transfers of Financial Assets (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Transfers of Financial Assets [Line Items]
Unpaid principal balance portfolio securitizations	$ 48,900,000,000	$ 32,500,000,000
Unconsolidated VIEs [Member]
Transfers of Financial Assets [Line Items]
Principal and interest received on retained interests	350,000,000	340,000,000
Unconsolidated VIEs [Member] | Single Class MBS, REMIC & Megas [Member]
Transfers of Financial Assets [Line Items]
Unpaid principal balance	6,100,000,000		6,300,000,000
Fair value	$ 7,500,000,000		$ 7,600,000,000