Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Financial assets
Restricted cash	$ 186	$ 169	$ 151
Loans subject to repurchase from Ginnie Mae	971	966
Financial liabilities
Unsecured senior notes, net	4,885	3,151
Advance, warehouse and MSR facilities, net	4,379	4,302
Nonrecurring Fair Value Measurements
Financial assets
Cash and cash equivalents	733	571
Restricted cash	186	169
Advances and other receivables, net	940	996
Loans subject to repurchase from Ginnie Mae	971	966
Financial liabilities
Unsecured senior notes, net	4,885	3,151
Advance, warehouse and MSR facilities, net	4,379	4,302
Liability for loans subject to repurchase from Ginnie Mae	971	966
Nonrecurring Fair Value Measurements | Level 1
Financial assets
Cash and cash equivalents	733	571
Restricted cash	186	169
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	971	966
Financial liabilities
Unsecured senior notes, net	4,963	3,056
Advance, warehouse and MSR facilities, net	4,402	4,318
Liability for loans subject to repurchase from Ginnie Mae	971	966
Nonrecurring Fair Value Measurements | Level 3
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net	940	996
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