Segment Information - Financial Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Revenues:
Service related, net	$ 472	$ 485	$ 912	$ 963
Net gain on mortgage loans held for sale	136	98	256	184
Total revenues	608	583	1,168	1,147
Total expenses	330	300	760	617
Other income (expenses)
Interest income	217	189	406	347
Interest Expense, Nonoperating	217	187	430	357
Other income (expenses), net	(1)	(8)	(12)	(11)
Total other income (expenses), net	(1)	(6)	(36)	(21)
Income before income tax expense	277	277	372	509
Depreciation and amortization for property and equipment and intangible assets	11	8	29	16
Total assets	18,499	15,783	18,499	15,783	$ 18,939
Salaries, wages and benefits	191	168	384	327
General and administrative	139	132	376	290
Operating Segments | Servicing
Revenues:
Service related, net	426	446	823	886
Net gain on mortgage loans held for sale	8	10	14	20
Total revenues	434	456	837	906
Total expenses	148	171	388	356
Other income (expenses)
Interest income	184	174	341	320
Interest Expense, Nonoperating	106	105	212	203
Other income (expenses), net	0	0	0	0
Total other income (expenses), net	78	69	129	117
Income before income tax expense	364	354	578	667
Depreciation and amortization for property and equipment and intangible assets	7	2	21	5
Total assets	14,412	12,759	14,412	12,759
Salaries, wages and benefits	89	84	179	169
General and administrative	59	87	209	187
Operating Segments | Originations
Revenues:
Service related, net	30	19	56	35
Net gain on mortgage loans held for sale	128	88	242	164
Total revenues	158	107	298	199
Total expenses	100	69	195	131
Other income (expenses)
Interest income	33	15	62	27
Interest Expense, Nonoperating	30	15	56	25
Other income (expenses), net	3	0	0	0
Total other income (expenses), net	6	0	6	2
Income before income tax expense	64	38	109	70
Depreciation and amortization for property and equipment and intangible assets	2	1	4	2
Total assets	2,481	1,398	2,481	1,398
Salaries, wages and benefits	56	40	108	74
General and administrative	44	29	87	57
Corporate/Other
Revenues:
Service related, net	16	20	33	42
Net gain on mortgage loans held for sale	0	0	0	0
Total revenues	16	20	33	42
Total expenses	82	60	177	130
Other income (expenses)
Interest income	0	0	3	0
Interest Expense, Nonoperating	81	67	162	129
Other income (expenses), net	(4)	(8)	(12)	(11)
Total other income (expenses), net	(85)	(75)	(171)	(140)
Income before income tax expense	(151)	(115)	(315)	(228)
Depreciation and amortization for property and equipment and intangible assets	2	5	4	9
Total assets	1,606	1,626	1,606	1,626
Salaries, wages and benefits	46	44	97	84
General and administrative	$ 36	$ 16	$ 80	$ 46