Fair Value Disclosures - Rollforward of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Non-agency MBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 432	$ 507
Included in earnings	(1)	9
Included in unrealized net holding gains (losses) in OCI	23	(18)
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	(13)	(18)
Transfers out of Level 3		0
Balance at end of period	441	480
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	(1)
MSRs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	1,056	1,052
Included in earnings	68	37
Included in unrealized net holding gains (losses) in OCI	0	0
Purchases	0	0
Issuances	37	38
Sales	0	0
Settlements	(42)	(39)
Transfers out of Level 3		0
Balance at end of period	1,119	1,088
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	68
Net Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	3	(13)
Included in earnings	0	(4)
Included in unrealized net holding gains (losses) in OCI	0	0
Purchases	0	0
Issuances	(5)	15
Sales	0	0
Settlements	9	12
Transfers out of Level 3		0
Balance at end of period	7	10
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	5
Private Equity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	404	362
Included in earnings	6	5
Included in unrealized net holding gains (losses) in OCI	0	0
Purchases	24	68
Issuances	0	0
Sales	(24)	(18)
Settlements	(10)	(4)
Transfers out of Level 3		(13)
Balance at end of period	400	$ 400
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	$ 12

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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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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- Definition

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

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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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