Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Financial assets
Reverse mortgage interests, net	$ 5,460	$ 6,279
Financial liabilities
Unsecured senior notes	2,167	2,366
Advance facilities	4,851	4,997
Other nonrecourse debt	4,671	5,286
Recurring Fair Value Measurements
Financial assets
Cash and cash equivalents	946	329
Restricted cash	229	283
Advances and other receivables, net	745	988
Financial liabilities
Advance facilities	4,851	4,997
Recurring Fair Value Measurements \| Level 1
Financial assets
Cash and cash equivalents	946	329
Restricted cash	229	283
Advances and other receivables, net	0	0
Financial liabilities
Advance facilities	0	0
Recurring Fair Value Measurements \| Level 2
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net	0	0
Financial liabilities
Advance facilities	4,851	4,997
Recurring Fair Value Measurements \| Level 3
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net	745	988
Financial liabilities
Advance facilities	0	0
Nonrecurring fair value measurements
Financial assets
Reverse mortgage interests, net	5,460	6,279
Financial liabilities
Unsecured senior notes	2,167	2,366
Nonrecurring fair value measurements \| Participating interest financing
Financial liabilities
Other nonrecourse debt	3,676	4,299
Nonrecurring fair value measurements \| Trust 2020-1
Financial liabilities
Other nonrecourse debt	513
Nonrecurring fair value measurements \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	257	331
Nonrecurring fair value measurements \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	225	300
Nonrecurring fair value measurements \| Trust 2018-3
Financial liabilities
Other nonrecourse debt		208
Nonrecurring fair value measurements \| Trust 2018-2
Financial liabilities
Other nonrecourse debt		148
Nonrecurring fair value measurements \| Level 1
Financial assets
Reverse mortgage interests, net	0	0
Financial liabilities
Unsecured senior notes	2,237	2,505
Nonrecurring fair value measurements \| Level 1 \| Participating interest financing
Financial liabilities
Other nonrecourse debt	0	0
Nonrecurring fair value measurements \| Level 1 \| Trust 2020-1
Financial liabilities
Other nonrecourse debt	0
Nonrecurring fair value measurements \| Level 1 \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	0	0
Nonrecurring fair value measurements \| Level 1 \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	0	0
Nonrecurring fair value measurements \| Level 1 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt		0
Nonrecurring fair value measurements \| Level 1 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt		0
Nonrecurring fair value measurements \| Level 2
Financial assets
Reverse mortgage interests, net	0	0
Financial liabilities
Unsecured senior notes	0	0
Nonrecurring fair value measurements \| Level 2 \| Participating interest financing
Financial liabilities
Other nonrecourse debt	0	0
Nonrecurring fair value measurements \| Level 2 \| Trust 2020-1
Financial liabilities
Other nonrecourse debt	0
Nonrecurring fair value measurements \| Level 2 \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	0	0
Nonrecurring fair value measurements \| Level 2 \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	0	0
Nonrecurring fair value measurements \| Level 2 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt		0
Nonrecurring fair value measurements \| Level 2 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt		0
Nonrecurring fair value measurements \| Level 3
Financial assets
Reverse mortgage interests, net	5,574	6,318
Financial liabilities
Unsecured senior notes	0	0
Nonrecurring fair value measurements \| Level 3 \| Participating interest financing
Financial liabilities
Other nonrecourse debt	3,679	4,299
Nonrecurring fair value measurements \| Level 3 \| Trust 2020-1
Financial liabilities
Other nonrecourse debt	513
Nonrecurring fair value measurements \| Level 3 \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	257	331
Nonrecurring fair value measurements \| Level 3 \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	$ 225	300
Nonrecurring fair value measurements \| Level 3 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt		208
Nonrecurring fair value measurements \| Level 3 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt		$ 148

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