Segment Information - Financial Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Revenues:
Service related, net	$ 478	$ 261
Net gain on mortgage loans held for sale	86	69
Total revenues	564	330
Total expenses	317	261
Other income (expenses)
Interest income	158	85
Interest expense	(170)	(110)
Other expenses, net	(3)	(9)
Total other income (expenses), net	(15)	(34)
Income before income tax expense (benefit)	232	35
Depreciation and amortization for property and equipment and intangible assets	8	9
Total assets	14,775	12,657	$ 14,196
Operating Segments | Servicing
Revenues:
Service related, net	440	231
Net gain on mortgage loans held for sale	10	0
Total revenues	450	231
Total expenses	185	153
Other income (expenses)
Interest income	146	79
Interest expense	(98)	(63)
Other expenses, net	0	0
Total other income (expenses), net	48	16
Income before income tax expense (benefit)	313	94
Depreciation and amortization for property and equipment and intangible assets	3	2
Total assets	12,187	10,050
Operating Segments | Originations
Revenues:
Service related, net	16	11
Net gain on mortgage loans held for sale	76	69
Total revenues	92	80
Total expenses	62	56
Other income (expenses)
Interest income	12	6
Interest expense	(10)	(7)
Other expenses, net	0	0
Total other income (expenses), net	2	(1)
Income before income tax expense (benefit)	32	23
Depreciation and amortization for property and equipment and intangible assets	1	2
Total assets	973	760
Corporate/Other
Revenues:
Service related, net	22	19
Net gain on mortgage loans held for sale	0	0
Total revenues	22	19
Total expenses	70	52
Other income (expenses)
Interest income	0	0
Interest expense	(62)	(40)
Other expenses, net	(3)	(9)
Total other income (expenses), net	(65)	(49)
Income before income tax expense (benefit)	(113)	(82)
Depreciation and amortization for property and equipment and intangible assets	4	5
Total assets	$ 1,615	$ 1,847