Consolidations and Transfers of Financial Assets Transfers of Financial Assets (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Transfers of Financial Assets [Line Items]
Portfolio securitizations: unpaid principal balance	$ 264.7	$ 212.0	$ 160.4
Unconsolidated VIEs [Member]
Transfers of Financial Assets [Line Items]
Retained interests: principal and interest received	1.2	1.2	$ 1.5
Unconsolidated VIEs [Member] | Single Class MBS, REMIC & Megas [Member]
Transfers of Financial Assets [Line Items]
Retained interests: unpaid principal balance	4.4	5.5
Retained interest: fair value	$ 5.8	$ 6.8