Fair Value Measurements - Reconciliation of Level 3 (Details) - USD ($) $ in Millions	5 Months Ended	7 Months Ended	12 Months Ended
Dec. 31, 2018	Jul. 31, 2018	Dec. 31, 2017
Excess spread financing
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	$ 1,039
Total gains or losses included in earnings	5
Payments received from borrowers	0
Purchases, issuances, sales and settlements
Purchases	0
Issuances	255
Sales	0
Repayments	(38)
Settlements	(77)
Changes in fair value	0
Balance - end of period	1,184	$ 1,039
Mortgage servicing rights financing
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	26
Total gains or losses included in earnings	6
Payments received from borrowers	0
Purchases, issuances, sales and settlements
Purchases	0
Issuances	0
Sales	0
Repayments	0
Settlements	0
Changes in fair value	0
Balance - end of period	32	26
Forward mortgage servicing rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	3,413
Total gains or losses included in earnings	(236)
Payments received from borrowers	0
Purchases, issuances, sales and settlements
Purchases	479
Issuances	120
Sales	(111)
Repayments	0
Settlements	0
Changes in fair value	0
Balance - end of period	3,665	3,413
Mortgage loans held for investment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	125
Total gains or losses included in earnings	(3)
Payments received from borrowers	(5)
Purchases, issuances, sales and settlements
Purchases	0
Issuances	0
Sales	0
Repayments	0
Settlements	0
Changes in fair value	2
Balance - end of period	119	125
Predecessor \| Excess spread financing
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	1,039	996	$ 1,214
Total gains or losses included in earnings		81	12
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		70	0
Sales		0	0
Repayments		(3)	(23)
Settlements		(105)	(207)
Balance - end of period		1,039	996
Predecessor \| Mortgage servicing rights financing
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	26	10	27
Total gains or losses included in earnings		16	(17)
Purchases, issuances, sales and settlements
Purchases		0	0
Issuances		0	0
Sales		0	0
Repayments			0
Settlements		0	0
Balance - end of period		26	10
Predecessor \| Forward mortgage servicing rights
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - beginning of period	$ 3,413	2,937	3,160
Total gains or losses included in earnings		166	(432)
Purchases, issuances, sales and settlements
Purchases		144	66
Issuances		162	203
Sales		4	(60)
Repayments		0	0
Settlements		0	0
Balance - end of period		$ 3,413	$ 2,937

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Payments From Borrowers

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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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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 increase (decrease) 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 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 gain (loss) recognized on the income statement for financial instrument classified as a liability 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 a liability 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 increase (decrease) of financial instrument classified as a liability 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 a liability 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 sales of financial instrument classified as a liability 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 settlements of financial instrument classified as a liability 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 a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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