Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Financial assets
Restricted cash	$ 332.0
Reverse mortgage interests, net	8,886.0
Mortgage loans held for sale	1,681.0
Mortgage loans held for investment, net	122.0
Financial liabilities
Unsecured senior notes	2,457.0
Advance facilities	596.0
Warehouse facilities	2,888.0
Mortgage servicing rights financing liability	26.0	$ 10.0
Excess spread financing	1,097.0
Derivative financial instruments at fair value	2.0
Other nonrecourse debt	7,165.0
Participating Interest Financing
Financial liabilities
Other nonrecourse debt	6,021.0
Trust 2016-2
Financial liabilities
Other nonrecourse debt	0.0
Trust 2016-3
Financial liabilities
Other nonrecourse debt	0.0
Trust 2017-1
Financial liabilities
Other nonrecourse debt	151.0
Trust 2017-2
Financial liabilities
Other nonrecourse debt	258.0
Trust 2018-1
Financial liabilities
Other nonrecourse debt	329.0
Trust 2018-2
Financial liabilities
Other nonrecourse debt	292.0
Legacy Asset
Financial liabilities
Other nonrecourse debt	32.0
Recurring Fair Value Measurements
Financial assets
Cash and cash equivalents	198.0
Restricted cash	332.0
Advances and other receivables, net	1,174.0
Reverse mortgage interests, net	8,886.0
Mortgage loans held for sale	1,681.1
Mortgage loans held for investment, net	121.6
Derivative financial instruments	72.0
Financial liabilities
Unsecured senior notes	2,457.0
Advance facilities	596.0
Warehouse facilities	2,888.0
Mortgage servicing rights financing liability	26.3
Excess spread financing	1,097.0
Derivative financial instruments at fair value	2.0
Recurring Fair Value Measurements \| Participating Interest Financing
Financial liabilities
Other nonrecourse debt	6,103.0
Recurring Fair Value Measurements \| Legacy Asset
Financial liabilities
Other nonrecourse debt	32.0
Recurring Fair Value Measurements \| Level 1
Financial assets
Cash and cash equivalents	198.0
Restricted cash	332.0
Advances and other receivables, net	0.0
Reverse mortgage interests, net	0.0
Mortgage loans held for sale	0.0
Mortgage loans held for investment, net	0.0
Derivative financial instruments	0.0
Financial liabilities
Unsecured senior notes	2,583.0
Advance facilities	0.0
Warehouse facilities	0.0
Mortgage servicing rights financing liability	0.0
Excess spread financing	0.0
Derivative financial instruments at fair value	0.0
Recurring Fair Value Measurements \| Level 1 \| Participating Interest Financing
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 1 \| Trust 2017-1
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 1 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 1 \| Trust 2018-1
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 1 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 1 \| Legacy Asset
Financial liabilities
Other nonrecourse debt	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
Reverse mortgage interests, net	0.0
Mortgage loans held for sale	1,681.1
Mortgage loans held for investment, net	0.0
Derivative financial instruments	72.0
Financial liabilities
Unsecured senior notes	0.0
Advance facilities	596.0
Warehouse facilities	2,888.0
Mortgage servicing rights financing liability	0.0
Excess spread financing	0.0
Derivative financial instruments at fair value	2.0
Recurring Fair Value Measurements \| Level 2 \| Participating Interest Financing
Financial liabilities
Other nonrecourse debt	6,101.0
Recurring Fair Value Measurements \| Level 2 \| Trust 2017-1
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 2 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 2 \| Trust 2018-1
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 2 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 2 \| Legacy Asset
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 3
Financial assets
Cash and cash equivalents	0.0
Restricted cash	0.0
Advances and other receivables, net	1,174.0
Reverse mortgage interests, net	8,980.0
Mortgage loans held for sale	0.0
Mortgage loans held for investment, net	121.6
Derivative financial instruments	0.0
Financial liabilities
Unsecured senior notes	0.0
Advance facilities	0.0
Warehouse facilities	0.0
Mortgage servicing rights financing liability	26.3
Excess spread financing	1,097.0
Derivative financial instruments at fair value	0.0
Recurring Fair Value Measurements \| Level 3 \| Participating Interest Financing
Financial liabilities
Other nonrecourse debt	0.0
Recurring Fair Value Measurements \| Level 3 \| Trust 2017-1
Financial liabilities
Other nonrecourse debt	176.0
Recurring Fair Value Measurements \| Level 3 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt	283.0
Recurring Fair Value Measurements \| Level 3 \| Trust 2018-1
Financial liabilities
Other nonrecourse debt	318.0
Recurring Fair Value Measurements \| Level 3 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt	271.0
Recurring Fair Value Measurements \| Level 3 \| Legacy Asset
Financial liabilities
Other nonrecourse debt	$ 31.0
Predecessor
Financial assets
Restricted cash		360.0
Reverse mortgage interests, net		9,984.0
Mortgage loans held for sale		1,891.0
Mortgage loans held for investment, net		139.0
Financial liabilities
Unsecured senior notes		1,874.0
Advance facilities		855.0
Warehouse facilities		3,285.0
Mortgage servicing rights financing liability		10.0
Excess spread financing		996.0
Derivative financial instruments at fair value		5.0
Other nonrecourse debt		8,014.0
Predecessor \| Participating Interest Financing
Financial liabilities
Other nonrecourse debt		7,111.0
Predecessor \| Trust 2016-2
Financial liabilities
Other nonrecourse debt		94.0
Predecessor \| Trust 2016-3
Financial liabilities
Other nonrecourse debt		138.0
Predecessor \| Trust 2017-1
Financial liabilities
Other nonrecourse debt		213.0
Predecessor \| Trust 2017-2
Financial liabilities
Other nonrecourse debt		365.0
Predecessor \| Trust 2018-1
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Trust 2018-2
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Legacy Asset
Financial liabilities
Other nonrecourse debt		42.0
Predecessor \| Recurring Fair Value Measurements
Financial assets
Cash and cash equivalents		215.0
Restricted cash		360.0
Advances and other receivables, net		1,706.0
Reverse mortgage interests, net		9,984.0
Mortgage loans held for sale		1,890.8
Mortgage loans held for investment, net		139.0
Derivative financial instruments		65.0
Financial liabilities
Unsecured senior notes		1,874.0
Advance facilities		855.0
Warehouse facilities		3,285.0
Mortgage servicing rights financing liability		9.5
Excess spread financing		996.0
Derivative financial instruments at fair value		5.0
Predecessor \| Recurring Fair Value Measurements \| Participating Interest Financing
Financial liabilities
Other nonrecourse debt		7,167.0
Predecessor \| Recurring Fair Value Measurements \| Trust 2016-2
Financial liabilities
Other nonrecourse debt		94.0
Predecessor \| Recurring Fair Value Measurements \| Trust 2016-3
Financial liabilities
Other nonrecourse debt		138.0
Predecessor \| Recurring Fair Value Measurements \| Legacy Asset
Financial liabilities
Other nonrecourse debt		37.0
Predecessor \| Recurring Fair Value Measurements \| Level 1
Financial assets
Cash and cash equivalents		215.0
Restricted cash		360.0
Advances and other receivables, net		0.0
Reverse mortgage interests, net		0.0
Mortgage loans held for sale		0.0
Mortgage loans held for investment, net		0.0
Derivative financial instruments		0.0
Financial liabilities
Unsecured senior notes		1,912.0
Advance facilities		0.0
Warehouse facilities		0.0
Mortgage servicing rights financing liability		0.0
Excess spread financing		0.0
Derivative financial instruments at fair value		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 1 \| Participating Interest Financing
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 1 \| Trust 2016-2
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 1 \| Trust 2016-3
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 1 \| Trust 2017-1
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 1 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 1 \| Legacy Asset
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| 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
Reverse mortgage interests, net		0.0
Mortgage loans held for sale		1,890.8
Mortgage loans held for investment, net		0.0
Derivative financial instruments		65.0
Financial liabilities
Unsecured senior notes		0.0
Advance facilities		855.0
Warehouse facilities		3,286.0
Mortgage servicing rights financing liability		0.0
Excess spread financing		0.0
Derivative financial instruments at fair value		5.0
Predecessor \| Recurring Fair Value Measurements \| Level 2 \| Participating Interest Financing
Financial liabilities
Other nonrecourse debt		7,353.0
Predecessor \| Recurring Fair Value Measurements \| Level 2 \| Trust 2016-2
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 2 \| Trust 2016-3
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 2 \| Trust 2017-1
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 2 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 2 \| Legacy Asset
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 3
Financial assets
Cash and cash equivalents		0.0
Restricted cash		0.0
Advances and other receivables, net		1,706.0
Reverse mortgage interests, net		10,164.0
Mortgage loans held for sale		0.0
Mortgage loans held for investment, net		139.0
Derivative financial instruments		0.0
Financial liabilities
Unsecured senior notes		0.0
Advance facilities		0.0
Warehouse facilities		0.0
Mortgage servicing rights financing liability		9.5
Excess spread financing		996.0
Derivative financial instruments at fair value		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 3 \| Participating Interest Financing
Financial liabilities
Other nonrecourse debt		0.0
Predecessor \| Recurring Fair Value Measurements \| Level 3 \| Trust 2016-2
Financial liabilities
Other nonrecourse debt		112.0
Predecessor \| Recurring Fair Value Measurements \| Level 3 \| Trust 2016-3
Financial liabilities
Other nonrecourse debt		155.0
Predecessor \| Recurring Fair Value Measurements \| Level 3 \| Trust 2017-1
Financial liabilities
Other nonrecourse debt		225.0
Predecessor \| Recurring Fair Value Measurements \| Level 3 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt		371.0
Predecessor \| Recurring Fair Value Measurements \| Level 3 \| Legacy Asset
Financial liabilities
Other nonrecourse debt		$ 36.0

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