Fair Value Disclosures - Rollforward of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Non-agency MBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 432	$ 507	$ 626
Included in earnings	9	36	25
Included in unrealized net holding gains (losses) in OCI		(40)	(45)
Purchases	0	0	0
Issuances	0	0	0
Sales	0	0	0
Settlements	(50)	(71)	(99)
Transfers out of Level 3		0
Adoption of fair value option for commercial MSRs			0
Ending balance	391	432	507
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	9
MSRs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,056	1,052	880
Included in earnings	71	48	63
Included in unrealized net holding gains (losses) in OCI		0	0
Purchases	0	0	0
Issuances	152	124	146
Sales	0	0	0
Settlements	(171)	(168)	(160)
Transfers out of Level 3		0
Adoption of fair value option for commercial MSRs			123
Ending balance	1,108	1,056	1,052
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	71
Net Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	3	(13)	4
Included in earnings	11	38	97
Included in unrealized net holding gains (losses) in OCI		0	0
Purchases	0	0	0
Issuances	24	43	82
Sales	0	0	0
Settlements	(26)	(65)	(196)
Transfers out of Level 3		0
Adoption of fair value option for commercial MSRs			0
Ending balance	12	3	(13)
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	12
Private Equity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	404	362	289
Included in earnings	66	58	20
Included in unrealized net holding gains (losses) in OCI		0	0
Purchases	91	142	106
Issuances	0	0	0
Sales	(112)	(119)	(4)
Settlements	(56)	(26)	(49)
Transfers out of Level 3		(13)
Adoption of fair value option for commercial MSRs			0
Ending balance	393	$ 404	$ 362
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	$ 11

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Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of issuances of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Amount of unrealized gain (loss) recognized in the income statement for a financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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