Segment Information - Financial Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Revenues:
Service related, net	$ 485	$ 402	$ 963	$ 663
Net gain on mortgage loans held for sale	98	84	184	153
Total revenues	583	486	1,147	816
Total expenses	300	278	617	539
Other income (expenses)
Interest income	189	117	347	202
Interest expense	(187)	(122)	(357)	(232)
Other expenses, net	(8)	(5)	(11)	(14)
Total other income (expenses), net	(6)	(10)	(21)	(44)
Income before income tax expense	277	198	509	233
Depreciation and amortization for property and equipment and intangible assets	8	9	16	18
Total assets	15,783	13,144	15,783	13,144	$ 14,196
Operating Segments | Servicing
Revenues:
Service related, net	446	365	886	596
Net gain on mortgage loans held for sale	10	3	20	3
Total revenues	456	368	906	599
Total expenses	171	159	356	312
Other income (expenses)
Interest income	174	107	320	186
Interest expense	(105)	(73)	(203)	(136)
Other expenses, net	0	0	0	0
Total other income (expenses), net	69	34	117	50
Income before income tax expense	354	243	667	337
Depreciation and amortization for property and equipment and intangible assets	2	3	5	5
Total assets	12,759	10,231	12,759	10,231
Operating Segments | Originations
Revenues:
Service related, net	19	16	35	27
Net gain on mortgage loans held for sale	88	81	164	150
Total revenues	107	97	199	177
Total expenses	69	59	131	115
Other income (expenses)
Interest income	15	10	27	16
Interest expense	(15)	(10)	(25)	(17)
Other expenses, net	0	0	0	0
Total other income (expenses), net	0	0	2	(1)
Income before income tax expense	38	38	70	61
Depreciation and amortization for property and equipment and intangible assets	1	2	2	4
Total assets	1,398	1,086	1,398	1,086
Corporate/Other
Revenues:
Service related, net	20	21	42	40
Net gain on mortgage loans held for sale	0	0	0	0
Total revenues	20	21	42	40
Total expenses	60	60	130	112
Other income (expenses)
Interest income	0	0	0	0
Interest expense	(67)	(39)	(129)	(79)
Other expenses, net	(8)	(5)	(11)	(14)
Total other income (expenses), net	(75)	(44)	(140)	(93)
Income before income tax expense	(115)	(83)	(228)	(165)
Depreciation and amortization for property and equipment and intangible assets	5	4	9	9
Total assets	$ 1,626	$ 1,827	$ 1,626	$ 1,827