Mortgage Servicing Rights ("MSRs") and Related Liabilities - Servicing Revenue (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended	7 Months Ended	9 Months Ended
	Jul. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Jul. 31, 2018	Sep. 30, 2017
Mortgage Servicing Rights [Line Items]
Contractually specified servicing fees		$ 163
Other service-related income		18
Incentive and modification income		8
Late fees		14
Reverse servicing fees		13
Mark-to-market adjustments		24
Counterparty revenue share		(26)
Amortization, net of accretion		(31)
Total servicing revenue		$ 183
Predecessor
Mortgage Servicing Rights [Line Items]
Contractually specified servicing fees	$ 79		$ 251	$ 574	$ 759
Other service-related income	10		40	66	126
Incentive and modification income	4		19	37	63
Late fees	7		22	53	67
Reverse servicing fees	4		16	37	43
Mark-to-market adjustments	25		(44)	196	(160)
Counterparty revenue share	(16)		(53)	(111)	(174)
Amortization, net of accretion	(16)		(60)	(112)	(187)
Total servicing revenue	$ 97		$ 191	$ 740	$ 537