Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Financial assets
Restricted cash	$ 133	$ 175	$ 130
Loans subject to repurchase from Ginnie Mae	1,889	1,865
Financial liabilities
Unsecured senior notes, net	2,675	2,673
Advance and warehouse facilities, net	2,934	2,885
Nonrecurring Fair Value Measurements
Financial assets
Cash and cash equivalents	534	527
Restricted cash	133	175
Advances and other receivables, net	933	1,019
Loans subject to repurchase from Ginnie Mae	1,889	1,865
Financial liabilities
Unsecured senior notes, net	2,675	2,673
Advance and warehouse facilities, net	2,934	2,885
Liability for loans subject to repurchase from Ginnie Mae	1,889	1,865
Nonrecurring Fair Value Measurements | Level 1
Financial assets
Cash and cash equivalents	534	527
Restricted cash	133	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 and warehouse 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	1,889	1,865
Financial liabilities
Unsecured senior notes, net	2,243	2,209
Advance and warehouse facilities, net	2,947	2,896
Liability for loans subject to repurchase from Ginnie Mae	1,889	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	933	1,019
Loans subject to repurchase from Ginnie Mae	0	0
Financial liabilities
Unsecured senior notes, net	0	0
Advance and warehouse facilities, net	0	0
Liability for loans subject to repurchase from Ginnie Mae	$ 0	$ 0