Consolidations and Transfers of Financial Assets Transfers of Financial Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Transfers of Financial Assets [Line Items]
Portfolio securitizations: unpaid principal balance	$ 68,100	$ 76,100	$ 194,500	$ 188,700
Unconsolidated VIEs [Member]
Transfers of Financial Assets [Line Items]
Retained interests: principal and interest received	294	$ 284	854	$ 907
Unconsolidated VIEs [Member] | Single Class MBS, REMIC & Megas [Member]
Transfers of Financial Assets [Line Items]
Retained interests: unpaid principal balance	4,000		4,000		$ 4,400
Retained interests: fair value	$ 5,000		$ 5,000		$ 5,800