Fair Value Measurements - Level 3 Reconciliation (Details) - USD ($) $ in Millions	2 Months Ended	7 Months Ended	9 Months Ended
Sep. 30, 2018	Jul. 31, 2018	Sep. 30, 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	26
Purchases	0
Issuances	84
Sales	0
Settlements	(31)
Repayments	21
Balance - end of period	1,097	$ 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	0
Purchases	0
Issuances	0
Sales	0
Settlements	0
Repayments	0
Balance - end of period	26	26
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	20
Purchases	72
Issuances	43
Sales	(63)
Settlements	0
Repayments	0
Balance - end of period	3,485	3,413
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	0
Purchases		0	0
Issuances		70	0
Sales		0	0
Settlements		(105)	(159)
Repayments		3	9
Balance - end of period		1,039	1,046
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	(7)
Purchases		0	0
Issuances		0	0
Sales		0	0
Settlements		0	0
Repayments			0
Balance - end of period		26	20
Predecessor \| 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	(361)
Purchases		144	30
Issuances		162	151
Sales		4	(24)
Settlements		0	0
Repayments		0	0
Balance - end of period		$ 3,413	$ 2,956

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Repayments

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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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