Fair Value Measurements - Level Three Measurements (Details) - Level Three - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
IRLCs, net
Activity in assets classified within Level Three of the valuation hierarchy
Balance, beginning of period	$ 3	$ 4	$ 4	$ 9
Purchases, Issuances, Sales and Settlements:
Purchases	0	0	0	0
Issuances	0	0	0	0
Sales	0	0	0	0
Settlements	(5)	(7)	(9)	(24)
Purchases, Issuances, Sales and Settlements Total	(5)	(7)	(9)	(24)
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	4	7	7	19
Transfers into Level Three	0	0	0	0
Transfers out of Level Three	0	0	0	0
Balance, end of period	2	4	2	4
IRLCs, net \| Gain on loans held for sale, net
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	4	7	7	19
IRLCs, net \| Change in fair value of MSRs
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0	0	0	0
IRLCs, net \| Net interest expense
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0	0	0	0
MLHS
Activity in assets classified within Level Three of the valuation hierarchy
Balance, beginning of period	8	32	9	47
Purchases, Issuances, Sales and Settlements:
Purchases	1	3	4	5
Issuances	0	2	0	3
Sales	(4)	(1)	(9)	(17)
Settlements	0	(6)	0	(9)
Purchases, Issuances, Sales and Settlements Total	(3)	(2)	(5)	(18)
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0	0	0	1
Transfers into Level Three	1	6	3	11
Transfers out of Level Three	(1)	(4)	(2)	(9)
Balance, end of period	5	32	5	32
MLHS \| Gain on loans held for sale, net
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0	0	0	0
MLHS \| Change in fair value of MSRs
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0	0	0	0
MLHS \| Net interest expense
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0	0	0	1
MSRs
Activity in assets classified within Level Three of the valuation hierarchy
Balance, beginning of period	496	596	476	690
Purchases, Issuances, Sales and Settlements:
Purchases	0	0	0	0
Issuances	0	7	3	18
Sales	(3)	(19)	(9)	(95)
Settlements	0	0	0	0
Purchases, Issuances, Sales and Settlements Total	(3)	(12)	(6)	(77)
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	(10)	(29)	13	(58)
Transfers into Level Three	0	0	0	0
Transfers out of Level Three	0	0	0	0
Balance, end of period	483	555	483	555
MSRs \| Gain on loans held for sale, net
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0	0	0	0
MSRs \| Change in fair value of MSRs
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	(10)	(29)	13	(58)
MSRs \| Net interest expense
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0	0	0	0
MSRs Secured Liability
Activity in assets classified within Level Three of the valuation hierarchy
Balance, beginning of period	(443)	0	(419)	0
Purchases, Issuances, Sales and Settlements:
Purchases	0	0	0	0
Issuances	0	(113)	0	(113)
Sales	0	0	0	0
Settlements	13	1	27	1
Purchases, Issuances, Sales and Settlements Total	13	(112)	27	(112)
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	(7)	(2)	(45)	(2)
Transfers into Level Three	0	0	0	0
Transfers out of Level Three	0	0	0	0
Balance, end of period	(437)	(114)	(437)	(114)
MSRs Secured Liability \| Gain on loans held for sale, net
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0	0	0	0
MSRs Secured Liability \| Change in fair value of MSRs
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	6	(1)	(18)	(1)
MSRs Secured Liability \| Net interest expense
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	(13)	$ (1)	(27)	$ (1)
Liability to Deliver MSRs
Activity in assets classified within Level Three of the valuation hierarchy
Balance, beginning of period	(1)		(2)
Purchases, Issuances, Sales and Settlements:
Purchases	0		0
Issuances	0		0
Sales	0		0
Settlements	1		3
Purchases, Issuances, Sales and Settlements Total	1		3
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	(1)		(2)
Transfers into Level Three	0		0
Transfers out of Level Three	0		0
Balance, end of period	(1)		(1)
Liability to Deliver MSRs \| Gain on loans held for sale, net
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	(1)		(2)
Liability to Deliver MSRs \| Change in fair value of MSRs
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	0		0
Liability to Deliver MSRs \| Net interest expense
Realized and unrealized gains (losses) included in:
Realized and unrealized gains (losses)	$ 0		$ 0

Fair Value, Realized and Unrealized Gains (Losses) Included in Level 3 of Valuation Hierarchy [Abstract]

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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
-Paragraph 2
-Subparagraph (c)(1)
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- Definition

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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

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.

+ References

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-Publisher FASB
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- Definition

Amount of purchases, (sales), issuances and (settlements) 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.

+ References

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-Publisher FASB
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- Definition

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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-Publisher FASB
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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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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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-Name Accounting Standards Codification
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- Definition

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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