Consolidations and Transfers of Financial Assets Transfers of Financial Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Transfers of Financial Assets [Line Items]
Portfolio securitizations: unpaid principal balance	$ 278,600	$ 228,400	$ 252,700
Unconsolidated VIEs [Member]
Transfers of Financial Assets [Line Items]
Retained interests: principal and interest received	595	585	$ 1,100
Unconsolidated VIEs [Member] | Single Class MBS, REMIC & Megas [Member]
Transfers of Financial Assets [Line Items]
Retained interests: unpaid principal balance	2,900	1,500
Retained interest: fair value	$ 4,000	$ 2,200