Consolidations and Transfers of Financial Assets Transfers of Financial Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Transfers of Financial Assets [Line Items]
Portfolio securitizations: unpaid principal balance	$ 228,400	$ 252,700	$ 264,700
Unconsolidated VIEs [Member]
Transfers of Financial Assets [Line Items]
Retained interests: principal and interest received	585	1,100	$ 1,200
Unconsolidated VIEs [Member] | Single Class MBS, REMIC & Megas [Member]
Transfers of Financial Assets [Line Items]
Retained interests: unpaid principal balance	1,500	3,900
Retained interest: fair value	$ 2,200	$ 4,700