Consolidations and Transfers of Financial Assets Transfers of Financial Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Transfers of Financial Assets [Line Items]
Document Period End Date			Sep. 30, 2019
Portfolio securitizations: unpaid principal balance	$ 89,000	$ 64,900	$ 187,700	$ 180,800
Unconsolidated VIEs [Member]
Transfers of Financial Assets [Line Items]
Retained interests: principal and interest received	187	$ 114	425	$ 468
Unconsolidated VIEs [Member] | Single Class MBS, REMIC & Megas [Member]
Transfers of Financial Assets [Line Items]
Retained interests: unpaid principal balance	3,100		3,100		$ 1,500
Retained interests: fair value	$ 4,200		$ 4,200		$ 2,200