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, 2019	Jul. 31, 2018	Sep. 30, 2019
Mortgage Servicing Rights [Line Items]
Contractually specified servicing fees		$ 163	$ 305		$ 893
Other service-related income		18	51		133
Incentive and modification income		8	12		29
Late fees		14	30		82
Reverse servicing fees		13	7		24
Mark-to-market adjustments		24	(83)		(607)
Counterparty revenue share		(26)	(86)		(204)
Amortization, net of accretion		(31)	(73)		(152)
Total servicing revenue		$ 183	$ 163		$ 198
Nationstar Mortgage Holdings Inc.
Mortgage Servicing Rights [Line Items]
Contractually specified servicing fees	$ 79			$ 574
Other service-related income	10			66
Incentive and modification income	4			37
Late fees	7			53
Reverse servicing fees	4			37
Mark-to-market adjustments	25			196
Counterparty revenue share	(16)			(111)
Amortization, net of accretion	(16)			(112)
Total servicing revenue	$ 97			$ 740