Segment Information - Financial Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Revenues:
Service related, net	$ 440	$ 478
Net gain on mortgage loans held for sale	120	86
Total revenues	560	564
Total expenses	430	317
Other income (expenses)
Interest income	189	158
Interest Expense, Nonoperating	213	170
Other expenses, net	(11)	(3)
Total other income (expenses), net	(35)	(15)
Income before income tax expense	95	232
Depreciation and amortization for property and equipment and intangible assets	18	8
Total assets	18,446	14,775	$ 18,939
Salaries, wages and benefits	193	159
General and administrative	237	158
Operating Segments | Servicing
Revenues:
Service related, net	397	440
Net gain on mortgage loans held for sale	6	10
Total revenues	403	450
Total expenses	240	185
Other income (expenses)
Interest income	157	146
Interest Expense, Nonoperating	106	98
Other expenses, net	0	0
Total other income (expenses), net	51	48
Income before income tax expense	214	313
Depreciation and amortization for property and equipment and intangible assets	14	3
Total assets	14,288	12,187
Salaries, wages and benefits	90	85
General and administrative	150	100
Operating Segments | Originations
Revenues:
Service related, net	26	16
Net gain on mortgage loans held for sale	114	76
Total revenues	140	92
Total expenses	95	62
Other income (expenses)
Interest income	29	12
Interest Expense, Nonoperating	26	10
Other expenses, net	(3)	0
Total other income (expenses), net	0	2
Income before income tax expense	45	32
Depreciation and amortization for property and equipment and intangible assets	2	1
Total assets	2,480	973
Salaries, wages and benefits	52	34
General and administrative	43	28
Corporate/Other
Revenues:
Service related, net	17	22
Net gain on mortgage loans held for sale	0	0
Total revenues	17	22
Total expenses	95	70
Other income (expenses)
Interest income	3	0
Interest Expense, Nonoperating	81	62
Other expenses, net	(8)	(3)
Total other income (expenses), net	(86)	(65)
Income before income tax expense	(164)	(113)
Depreciation and amortization for property and equipment and intangible assets	2	4
Total assets	1,678	1,615
Salaries, wages and benefits	51	40
General and administrative	$ 44	$ 30