Consolidations and Transfers of Financial Assets Transfers of Financial Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Transfers of Financial Assets [Line Items]
Portfolio securitizations: unpaid principal balance	$ 69,200	$ 64,300	$ 126,500	$ 112,600
Unconsolidated VIEs [Member]
Transfers of Financial Assets [Line Items]
Retained interests: principal and interest received	303	$ 315	560	$ 623
Unconsolidated VIEs [Member] | Single Class MBS, REMIC & Megas [Member]
Transfers of Financial Assets [Line Items]
Retained interests: unpaid principal balance	4,100		4,100		$ 4,400
Retained interests: fair value	$ 5,200		$ 5,200		$ 5,800