Fair Value Disclosures - Rollforward of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Trading Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 3	$ 0	$ 0
Included in earnings	0	0	0
Included in unrealized net holding gains (losses) in OCI	0		0
Purchases	23	5	0
Issuances	0	0	0
Sales	(26)	(2)	0
Settlements	0	0	0
Transfers into Level 3	0
Transfers out of Level 3
Merger additions	0
Ending balance	0	3	0
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	0
Non-agency MBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	391	432	507
Included in earnings	13	9	36
Included in unrealized net holding gains (losses) in OCI	4		(40)
Purchases	0	0	0
Issuances	0	0	0
Sales	0	0	0
Settlements	(40)	(50)	(71)
Transfers into Level 3	0
Transfers out of Level 3			0
Merger additions	0
Ending balance	368	391	432
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	12
MSRs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,108	1,056	1,052
Included in earnings	(105)	71	48
Included in unrealized net holding gains (losses) in OCI	0		0
Purchases	31	0	0
Issuances	170	152	124
Sales	(27)	0	0
Settlements	(164)	(171)	(168)
Transfers into Level 3	0
Transfers out of Level 3			0
Merger additions	1,605
Ending balance	2,618	1,108	1,056
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	(105)
Net Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	12	3	(13)
Included in earnings	63	11	38
Included in unrealized net holding gains (losses) in OCI	0		0
Purchases	(1)	0	0
Issuances	63	24	43
Sales	0	0	0
Settlements	(118)	(26)	(65)
Transfers into Level 3	(10)
Transfers out of Level 3			0
Merger additions	10
Ending balance	19	12	3
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	24
Private Equity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	393	404	362
Included in earnings	47	66	58
Included in unrealized net holding gains (losses) in OCI	0		0
Purchases	137	91	142
Issuances	0	0	0
Sales	(91)	(112)	(119)
Settlements	(46)	(56)	(26)
Transfers into Level 3	0
Transfers out of Level 3			(13)
Merger additions	0
Ending balance	440	$ 393	$ 404
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	$ 16