Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Financial assets
Reverse mortgage interests, net	$ 5,253	$ 6,279
Financial liabilities
Unsecured senior notes, net	2,074	2,366
Advance and warehouse facilities, net	6,763	4,997
Non-recourse debt	4,424	5,286
Fair Value, Recurring
Financial assets
Cash and cash equivalents	695	329
Restricted cash	218	283
Advances and other receivables, net		988
Loans subject to repurchase from Ginnie Mae	6,159	560
Financial liabilities
Unsecured senior notes, net	2,074	2,366
Advance and warehouse facilities, net	6,763	4,997
Liability for loans subject to repurchase from Ginnie Mae	6,159	560
Fair Value, Recurring \| Level 1
Financial assets
Cash and cash equivalents	695	329
Restricted cash	218	283
Advances and other receivables, net		0
Loans subject to repurchase from Ginnie Mae	0	0
Financial liabilities
Unsecured senior notes, net	2,208	2,505
Advance and warehouse facilities, net	0	0
Liability for loans subject to repurchase from Ginnie Mae	0	0
Fair Value, Recurring \| Level 2
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net		0
Loans subject to repurchase from Ginnie Mae	6,159	560
Financial liabilities
Unsecured senior notes, net	0	0
Advance and warehouse facilities, net	6,774	4,997
Liability for loans subject to repurchase from Ginnie Mae	6,159	560
Fair Value, Recurring \| Level 3
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net		988
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
Fair Value, Nonrecurring
Financial assets
Advances and other receivables, net	940
Reverse mortgage interests, net	5,253	6,279
Fair Value, Nonrecurring \| Participating interest financing
Financial liabilities
Non-recourse debt	3,485	4,299
Fair Value, Nonrecurring \| Trust 2020-1
Financial liabilities
Non-recourse debt	488
Fair Value, Nonrecurring \| Trust 2019-2
Financial liabilities
Non-recourse debt		331
Fair Value, Nonrecurring \| Trust 2019-1
Financial liabilities
Non-recourse debt	240	300
Fair Value, Nonrecurring \| Trust 2018-3
Financial liabilities
Non-recourse debt	211	208
Fair Value, Nonrecurring \| Trust 2018-2
Financial liabilities
Non-recourse debt		148
Fair Value, Nonrecurring \| Level 1
Financial assets
Advances and other receivables, net	0
Reverse mortgage interests, net	0	0
Fair Value, Nonrecurring \| Level 1 \| Participating interest financing
Financial liabilities
Non-recourse debt	0	0
Fair Value, Nonrecurring \| Level 1 \| Trust 2020-1
Financial liabilities
Non-recourse debt
Fair Value, Nonrecurring \| Level 1 \| Trust 2019-2
Financial liabilities
Non-recourse debt		0
Fair Value, Nonrecurring \| Level 1 \| Trust 2019-1
Financial liabilities
Non-recourse debt	0	0
Fair Value, Nonrecurring \| Level 1 \| Trust 2018-3
Financial liabilities
Non-recourse debt	0	0
Fair Value, Nonrecurring \| Level 1 \| Trust 2018-2
Financial liabilities
Non-recourse debt		0
Fair Value, Nonrecurring \| Level 2
Financial assets
Advances and other receivables, net	0
Reverse mortgage interests, net	0	0
Fair Value, Nonrecurring \| Level 2 \| Participating interest financing
Financial liabilities
Non-recourse debt	0	0
Fair Value, Nonrecurring \| Level 2 \| Trust 2020-1
Financial liabilities
Non-recourse debt
Fair Value, Nonrecurring \| Level 2 \| Trust 2019-2
Financial liabilities
Non-recourse debt		0
Fair Value, Nonrecurring \| Level 2 \| Trust 2019-1
Financial liabilities
Non-recourse debt	0	0
Fair Value, Nonrecurring \| Level 2 \| Trust 2018-3
Financial liabilities
Non-recourse debt	0	0
Fair Value, Nonrecurring \| Level 2 \| Trust 2018-2
Financial liabilities
Non-recourse debt		0
Fair Value, Nonrecurring \| Level 3
Financial assets
Advances and other receivables, net	940
Reverse mortgage interests, net	5,383	6,318
Fair Value, Nonrecurring \| Level 3 \| Participating interest financing
Financial liabilities
Non-recourse debt	3,496	4,299
Fair Value, Nonrecurring \| Level 3 \| Trust 2020-1
Financial liabilities
Non-recourse debt	490
Fair Value, Nonrecurring \| Level 3 \| Trust 2019-2
Financial liabilities
Non-recourse debt		331
Fair Value, Nonrecurring \| Level 3 \| Trust 2019-1
Financial liabilities
Non-recourse debt	241	300
Fair Value, Nonrecurring \| Level 3 \| Trust 2018-3
Financial liabilities
Non-recourse debt	$ 212	208
Fair Value, Nonrecurring \| Level 3 \| Trust 2018-2
Financial liabilities
Non-recourse debt		$ 148

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