Fair Value Disclosures - Rollforward of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Non-agency MBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 441	$ 480	$ 432	$ 507
Included in earnings	7	14	6	23
Included in unrealized net holding gains (losses) in OCI	(9)	(2)	14	(20)
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(14)	(18)	(27)	(36)
Transfers out of Level 3				0
Ending balance	425	474	425	474
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	7		6
MSRs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	1,119	1,088	1,056	1,052
Included in earnings	23	(17)	91	20
Included in unrealized net holding gains (losses) in OCI	0	0	0	0
Purchases	0	0	0	0
Issuances	46	25	83	63
Sales	0	0	0	0
Settlements	(45)	(44)	(87)	(83)
Transfers out of Level 3				0
Ending balance	1,143	1,052	1,143	1,052
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	23		91
Net Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	7	10	3	(13)
Included in earnings	1	23	1	19
Included in unrealized net holding gains (losses) in OCI	0	0	0	0
Purchases	0	0	0	0
Issuances	11	9	6	24
Sales	0	0	0	0
Settlements	(15)	(39)	(6)	(27)
Transfers out of Level 3				0
Ending balance	4	3	4	3
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	4		4
Private Equity Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	400	400	404	362
Included in earnings	5	0	11	5
Included in unrealized net holding gains (losses) in OCI	0	0	0	0
Purchases	3	7	27	75
Issuances	0	0	0	0
Sales	0	(12)	(24)	(30)
Settlements	(9)	(1)	(19)	(5)
Transfers out of Level 3				(13)
Ending balance	399	$ 394	399	$ 394
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held	$ 4		$ 11

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 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 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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