Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Financial assets
Restricted cash	$ 148	$ 146	$ 118
Loans subject to repurchase from Ginnie Mae	1,575	1,496
Financial liabilities
Unsecured senior notes, net	2,673	2,670
Advance and warehouse facilities, net	3,070	4,997
Nonrecurring Fair Value Measurements
Financial assets
Cash and cash equivalents	530	895
Restricted cash	148	146
Advances and other receivables, net	831	1,228
Loans subject to repurchase from Ginnie Mae	1,575	1,496
Financial liabilities
Unsecured senior notes, net	2,673	2,670
Advance and warehouse facilities, net	3,070	4,997
Liability for loans subject to repurchase from Ginnie Mae	1,575	1,496
Nonrecurring Fair Value Measurements | Level 1
Financial assets
Cash and cash equivalents	530	895
Restricted cash	148	146
Advances and other receivables, net	0	0
Loans subject to repurchase from Ginnie Mae	0	0
Financial liabilities
Unsecured senior notes, net	2,085	2,737
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	1,575	1,496
Financial liabilities
Unsecured senior notes, net	0	0
Advance and warehouse facilities, net	3,076	5,009
Liability for loans subject to repurchase from Ginnie Mae	1,575	1,496
Nonrecurring Fair Value Measurements | Level 3
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net	831	1,228
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