Segment Information - Financial Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Revenues:
Service related, net	$ 288	$ 432	$ 1,251	$ 1,095
Net gain on mortgage loans held for sale	136	142	320	295
Total revenues	424	574	1,571	1,390
Total expenses	335	301	952	840
Other income (expenses)
Interest income	227	167	574	369
Interest Expense, Nonoperating	199	146	556	378
Other expenses, net	(5)	58	(16)	44
Total other income (expenses), net	23	79	2	35
Income before income tax expense	112	352	621	585
Depreciation and amortization for property and equipment and intangible assets	9	10	25	28
Total assets	16,186	13,427	16,186	13,427	$ 14,196
Operating Segments | Servicing
Revenues:
Service related, net	246	392	1,132	988
Net gain on mortgage loans held for sale	10	72	30	75
Total revenues	256	464	1,162	1,063
Total expenses	180	172	536	484
Other income (expenses)
Interest income	201	157	521	343
Interest Expense, Nonoperating	100	88	303	224
Other expenses, net	0	0	0	0
Total other income (expenses), net	101	69	218	119
Income before income tax expense	177	361	844	698
Depreciation and amortization for property and equipment and intangible assets	2	4	7	9
Total assets	12,462	10,916	12,462	10,916
Operating Segments | Originations
Revenues:
Service related, net	24	18	59	45
Net gain on mortgage loans held for sale	126	70	290	220
Total revenues	150	88	349	265
Total expenses	83	58	214	173
Other income (expenses)
Interest income	25	10	52	26
Interest Expense, Nonoperating	23	11	48	28
Other expenses, net	0	0	0	0
Total other income (expenses), net	2	(1)	4	(2)
Income before income tax expense	69	29	139	90
Depreciation and amortization for property and equipment and intangible assets	0	2	2	6
Total assets	2,001	868	2,001	868
Corporate/Other
Revenues:
Service related, net	18	22	60	62
Net gain on mortgage loans held for sale	0	0	0	0
Total revenues	18	22	60	62
Total expenses	72	71	202	183
Other income (expenses)
Interest income	1	0	1	0
Interest Expense, Nonoperating	76	47	205	126
Other expenses, net	(5)	58	(16)	44
Total other income (expenses), net	(80)	11	(220)	(82)
Income before income tax expense	(134)	(38)	(362)	(203)
Depreciation and amortization for property and equipment and intangible assets	7	4	16	13
Total assets	$ 1,723	$ 1,643	$ 1,723	$ 1,643