Segment Information - Financial Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenues:
Service related, net	$ 1,788	$ 1,440	$ 1,865
Net gain on mortgage loans held for sale	437	354	599
Total revenues	2,225	1,794	2,464
Salaries, wages and benefits	695	634	789
General and administrative	624	538	485
Total expenses	1,319	1,172	1,274
Other Nonoperating Income (Expense) [Abstract]
Interest income	790	528	261
Interest Expense, Nonoperating	776	537	424
Other income (expenses), net	(19)	41	187
Total other income (expenses), net	(5)	32	24
Income before income tax expense	901	654	1,214
Depreciation and amortization for property and equipment and intangible assets	44	38	37
Total assets	18,939	14,196	12,776
Operating Segments | Servicing
Revenues:
Service related, net	1,625	1,295	1,691
Net gain on mortgage loans held for sale	39	84	(33)
Total revenues	1,664	1,379	1,658
Salaries, wages and benefits	339	340	324
General and administrative	382	324	235
Total expenses	721	664	559
Other Nonoperating Income (Expense) [Abstract]
Interest income	705	491	208
Interest Expense, Nonoperating	411	324	221
Other income (expenses), net	0	0	0
Total other income (expenses), net	294	167	(13)
Income before income tax expense	1,237	882	1,086
Depreciation and amortization for property and equipment and intangible assets	15	12	18
Total assets	14,900	11,740	10,152
Operating Segments | Originations
Revenues:
Service related, net	86	61	98
Net gain on mortgage loans held for sale	398	271	632
Total revenues	484	332	730
Salaries, wages and benefits	178	143	329
General and administrative	126	89	162
Total expenses	304	232	491
Other Nonoperating Income (Expense) [Abstract]
Interest income	84	36	53
Interest Expense, Nonoperating	79	37	43
Other income (expenses), net	0	0	0
Total other income (expenses), net	5	(1)	10
Income before income tax expense	185	99	249
Depreciation and amortization for property and equipment and intangible assets	2	8	16
Total assets	2,338	782	749
Corporate/ Other
Revenues:
Service related, net	77	84	76
Net gain on mortgage loans held for sale	0	(1)	0
Total revenues	77	83	76
Salaries, wages and benefits	178	151	136
General and administrative	116	125	88
Total expenses	294	276	224
Other Nonoperating Income (Expense) [Abstract]
Interest income	1	1	0
Interest Expense, Nonoperating	286	176	160
Other income (expenses), net	(19)	41	187
Total other income (expenses), net	(304)	(134)	27
Income before income tax expense	(521)	(327)	(121)
Depreciation and amortization for property and equipment and intangible assets	27	18	3
Total assets	$ 1,701	$ 1,674	$ 1,875