Fair Value Disclosures - Rollforward of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Trading and equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 3	$ 0
Included in earnings	0	0
Included in unrealized net holding gains (losses) in OCI	0	0
Purchases	15	0
Issuances	0	0
Sales	(7)	0
Settlements	0	0
Ending balance	11	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
Included in earnings	2	(1)
Included in unrealized net holding gains (losses) in OCI	1	23
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	(8)	(13)
Ending balance	386	441
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	2
MSRs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,108	1,056
Included in earnings	(54)	68
Included in unrealized net holding gains (losses) in OCI	0	0
Purchases	0	0
Issuances	22	37
Sales	0	0
Settlements	(40)	(42)
Ending balance	1,036	1,119
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	(54)
Net Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	12	3
Included in earnings	8	0
Included in unrealized net holding gains (losses) in OCI	0	0
Purchases	0	0
Issuances	17	(5)
Sales	0	0
Settlements	(30)	9
Ending balance	7	7
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	7
Private Equity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	393	404
Included in earnings	23	6
Included in unrealized net holding gains (losses) in OCI	0	0
Purchases	7	24
Issuances	0	0
Sales	(33)	(24)
Settlements	(2)	(10)
Ending balance	388	$ 400
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	$ 4

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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 gain (loss) recognized in other comprehensive income (loss) 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 purchases 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 settlement 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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Fair value 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 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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