Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Financial assets
Restricted cash	$ 151	$ 175	$ 148
Loans subject to repurchase from Ginnie Mae	1,027	1,865
Financial liabilities
Unsecured senior notes, net	3,147	2,673
Advance, warehouse and MSR facilities, net	3,545	2,885
Nonrecurring Fair Value Measurements
Financial assets
Cash and cash equivalents	553	527
Restricted cash	151	175
Advances and other receivables, net	758	1,019
Loans subject to repurchase from Ginnie Mae	1,027	1,865
Financial liabilities
Unsecured senior notes, net	3,147	2,673
Advance, warehouse and MSR facilities, net	3,545	2,885
Liability for loans subject to repurchase from Ginnie Mae	1,027	1,865
Nonrecurring Fair Value Measurements | Level 1
Financial assets
Cash and cash equivalents	553	527
Restricted cash	151	175
Advances and other receivables, net	0	0
Loans subject to repurchase from Ginnie Mae	0	0
Financial liabilities
Unsecured senior notes, net	0	0
Advance, warehouse and MSR facilities, net	0	0
Liability for loans subject to repurchase from Ginnie Mae	0	0
Nonrecurring Fair Value Measurements | Level 2
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net	0	0
Loans subject to repurchase from Ginnie Mae	1,027	1,865
Financial liabilities
Unsecured senior notes, net	2,815	2,209
Advance, warehouse and MSR facilities, net	3,560	2,896
Liability for loans subject to repurchase from Ginnie Mae	1,027	1,865
Nonrecurring Fair Value Measurements | Level 3
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net	758	1,019
Loans subject to repurchase from Ginnie Mae	0	0
Financial liabilities
Unsecured senior notes, net	0	0
Advance, warehouse and MSR facilities, net	0	0
Liability for loans subject to repurchase from Ginnie Mae	$ 0	$ 0