Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Financial assets
Loans subject to repurchase from Ginnie Mae	$ 1,496	$ 6,159
Financial liabilities
Unsecured senior notes, net	2,670	2,074
Advance and warehouse facilities, net	4,997	6,258
Fair Value, Nonrecurring
Financial assets
Cash and cash equivalents	895	695
Restricted cash	146	135
Advances and other receivables, net	1,228	940
Financial liabilities
Unsecured senior notes, net	2,670	2,074
Advance and warehouse facilities, net	4,997	6,258
Liability for loans subject to repurchase from Ginnie Mae	1,496	6,159
Fair Value, Nonrecurring | Level 1
Financial assets
Cash and cash equivalents	895	695
Restricted cash	146	135
Advances and other receivables, net	0	0
Loans subject to repurchase from Ginnie Mae	0	0
Financial liabilities
Unsecured senior notes, net	2,737	2,208
Advance and warehouse facilities, net	0	0
Liability for loans subject to repurchase from Ginnie Mae	0	0
Fair Value, Nonrecurring | 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	1,496	6,159
Financial liabilities
Unsecured senior notes, net	0	0
Advance and warehouse facilities, net	5,009	6,269
Liability for loans subject to repurchase from Ginnie Mae	1,496	6,159
Fair Value, Nonrecurring | Level 3
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net	1,228	940
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