Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financial assets
Reverse mortgage interests, net	$ 5,709	$ 6,279
Mortgage loans held for sale	3,179	4,077
Derivative financial instruments	391	153
Financial liabilities
Unsecured senior notes	2,261	2,366
Advance facilities	475	422
Warehouse facilities	4,031	4,575
Mortgage servicing rights financing liability	49	37
Excess spread financing	1,124	1,311
Derivative financial instruments	50	15
Other nonrecourse debt	4,707	5,286
Recurring Fair Value Measurements
Financial assets
Cash and cash equivalents	1,041	329
Restricted cash	260	283
Advances and other receivables, net	668	988
Mortgage loans held for sale	3,179	4,077
Derivative financial instruments	391	153
Financial liabilities
Advance facilities	475	422
Warehouse facilities	4,031	4,575
Mortgage servicing rights financing liability	49	37
Excess spread financing	1,124	1,311
Derivative financial instruments	50	15
Recurring Fair Value Measurements \| Level 1
Financial assets
Cash and cash equivalents	1,041	329
Restricted cash	260	283
Advances and other receivables, net	0	0
Mortgage loans held for sale	0	0
Derivative financial instruments	0	0
Financial liabilities
Advance facilities	0	0
Warehouse facilities	0	0
Mortgage servicing rights financing liability	0	0
Excess spread financing	0	0
Derivative financial instruments	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
Mortgage loans held for sale	3,179	4,077
Derivative financial instruments	3	153
Financial liabilities
Advance facilities	475	422
Warehouse facilities	4,031	4,575
Mortgage servicing rights financing liability	0	0
Excess spread financing	0	0
Derivative financial instruments	50	15
Recurring Fair Value Measurements \| Level 3
Financial assets
Cash and cash equivalents	0	0
Restricted cash	0	0
Advances and other receivables, net	668	988
Mortgage loans held for sale	0	0
Derivative financial instruments	388	0
Financial liabilities
Advance facilities	0	0
Warehouse facilities	0	0
Mortgage servicing rights financing liability	49	37
Excess spread financing	1,124	1,311
Derivative financial instruments	0	0
Nonrecurring fair value measurements
Financial assets
Reverse mortgage interests, net	5,709	6,279
Financial liabilities
Unsecured senior notes	2,261	2,366
Nonrecurring fair value measurements \| Participating interest financing
Financial liabilities
Other nonrecourse debt	3,886	4,299
Nonrecurring fair value measurements \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	272	331
Nonrecurring fair value measurements \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	243	300
Nonrecurring fair value measurements \| Trust 2018-3
Financial liabilities
Other nonrecourse debt	179	208
Nonrecurring fair value measurements \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	127	148
Nonrecurring fair value measurements \| Level 1
Financial assets
Reverse mortgage interests, net	0	0
Financial liabilities
Unsecured senior notes	2,307	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 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	0
Nonrecurring fair value measurements \| Level 1 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	0	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 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	0
Nonrecurring fair value measurements \| Level 2 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	0	0
Nonrecurring fair value measurements \| Level 3
Financial assets
Reverse mortgage interests, net	5,736	6,318
Financial liabilities
Unsecured senior notes	0	0
Nonrecurring fair value measurements \| Level 3 \| Participating interest financing
Financial liabilities
Other nonrecourse debt	3,857	4,299
Nonrecurring fair value measurements \| Level 3 \| Trust 2019-2
Financial liabilities
Other nonrecourse debt	272	331
Nonrecurring fair value measurements \| Level 3 \| Trust 2019-1
Financial liabilities
Other nonrecourse debt	243	300
Nonrecurring fair value measurements \| Level 3 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt	179	208
Nonrecurring fair value measurements \| Level 3 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	$ 127	$ 148

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