Fair Value Measurements - Fair Value by Balance Sheet Line Item (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financial assets
Restricted cash	$ 319.0
Reverse mortgage interests, net	7,934.0
Mortgage loans held for sale	1,631.0
Mortgage loans held for investment, net	119.0
Financial liabilities
Unsecured senior notes	2,459.0
Advance facilities, net	595.0
Warehouse facilities	2,349.0
Other nonrecourse debt, net	6,795.0
Participating interest financing
Financial liabilities
Other nonrecourse debt, net	5,607.0
Trust 2016-2
Financial liabilities
Other nonrecourse debt, net	0.0
Trust 2016-3
Financial liabilities
Other nonrecourse debt, net	0.0
Trust 2017-1
Financial liabilities
Other nonrecourse debt, net	0.0
Trust 2017-2
Financial liabilities
Other nonrecourse debt, net	231.0
Trust 2018-1
Financial liabilities
Other nonrecourse debt, net	284.0
Trust 2018-2
Financial liabilities
Other nonrecourse debt, net	250.0
Trust 2018-3
Financial liabilities
Other nonrecourse debt, net	326.0
Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net	29.0
Fair Value, Measurements, Recurring
Financial assets
Cash and cash equivalents	242.0
Restricted cash	319.0
Advances and other receivables, net	1,194.0
Reverse mortgage interests, net	7,934.0
Mortgage loans held for sale	1,630.8
Mortgage loans held for investment, net	119.1
Derivative financial instruments	49.0
Financial liabilities
Unsecured senior notes	2,459.0
Advance facilities, net	595.0
Warehouse facilities	2,349.0
Mortgage servicing rights financing liability	31.7
Excess spread financing	1,184.0
Derivative financial instruments	20.0
Fair Value, Measurements, Recurring \| Participating interest financing
Financial liabilities
Other nonrecourse debt, net	5,675.0
Fair Value, Measurements, Recurring \| Trust 2017-2
Financial liabilities
Other nonrecourse debt, net	231.0
Fair Value, Measurements, Recurring \| Trust 2018-1
Financial liabilities
Other nonrecourse debt, net	284.0
Fair Value, Measurements, Recurring \| Trust 2018-2
Financial liabilities
Other nonrecourse debt, net	250.0
Fair Value, Measurements, Recurring \| Trust 2018-3
Financial liabilities
Other nonrecourse debt, net	326.0
Fair Value, Measurements, Recurring \| Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net	29.0
Fair Value, Measurements, Recurring \| Level 1
Financial assets
Cash and cash equivalents	242.0
Restricted cash	319.0
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	2,451.0
Advance facilities, net	0.0
Warehouse facilities	0.0
Mortgage servicing rights financing liability	0.0
Excess spread financing	0.0
Derivative financial instruments	0.0
Fair Value, Measurements, Recurring \| Level 1 \| Participating interest financing
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 1 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 1 \| Trust 2018-1
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 1 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 1 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 1 \| Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| 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	1,630.8
Mortgage loans held for investment, net	0.0
Derivative financial instruments	49.0
Financial liabilities
Unsecured senior notes	0.0
Advance facilities, net	595.0
Warehouse facilities	2,349.0
Mortgage servicing rights financing liability	0.0
Excess spread financing	0.0
Derivative financial instruments	20.0
Fair Value, Measurements, Recurring \| Level 2 \| Participating interest financing
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 2 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 2 \| Trust 2018-1
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 2 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 2 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 2 \| Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net	0.0
Fair Value, Measurements, Recurring \| Level 3
Financial assets
Cash and cash equivalents	0.0
Restricted cash	0.0
Advances and other receivables, net	1,194.0
Reverse mortgage interests, net	7,942.0
Mortgage loans held for sale	0.0
Mortgage loans held for investment, net	119.1
Derivative financial instruments	0.0
Financial liabilities
Unsecured senior notes	0.0
Advance facilities, net	0.0
Warehouse facilities	0.0
Mortgage servicing rights financing liability	31.7
Excess spread financing	1,184.0
Derivative financial instruments	0.0
Fair Value, Measurements, Recurring \| Level 3 \| Participating interest financing
Financial liabilities
Other nonrecourse debt, net	5,672.0
Fair Value, Measurements, Recurring \| Level 3 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt, net	230.0
Fair Value, Measurements, Recurring \| Level 3 \| Trust 2018-1
Financial liabilities
Other nonrecourse debt, net	284.0
Fair Value, Measurements, Recurring \| Level 3 \| Trust 2018-2
Financial liabilities
Other nonrecourse debt, net	249.0
Fair Value, Measurements, Recurring \| Level 3 \| Trust 2018-3
Financial liabilities
Other nonrecourse debt, net	326.0
Fair Value, Measurements, Recurring \| Level 3 \| Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net	$ 28.0
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, net		855.0
Warehouse facilities		3,285.0
Mortgage servicing rights financing liability		9.5
Other nonrecourse debt, net		8,014.0
Predecessor \| Participating interest financing
Financial liabilities
Other nonrecourse debt, net		7,111.0
Predecessor \| Trust 2016-2
Financial liabilities
Other nonrecourse debt, net		94.0
Predecessor \| Trust 2016-3
Financial liabilities
Other nonrecourse debt, net		138.0
Predecessor \| Trust 2017-1
Financial liabilities
Other nonrecourse debt, net		213.0
Predecessor \| Trust 2017-2
Financial liabilities
Other nonrecourse debt, net		365.0
Predecessor \| Trust 2018-1
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Trust 2018-2
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Trust 2018-3
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net		42.0
Predecessor \| Fair Value, Measurements, Recurring
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, net		855.0
Warehouse facilities		3,285.0
Mortgage servicing rights financing liability		9.5
Excess spread financing		996.0
Derivative financial instruments		5.0
Predecessor \| Fair Value, Measurements, Recurring \| Participating interest financing
Financial liabilities
Other nonrecourse debt, net		7,167.0
Predecessor \| Fair Value, Measurements, Recurring \| Trust 2016-2
Financial liabilities
Other nonrecourse debt, net		94.0
Predecessor \| Fair Value, Measurements, Recurring \| Trust 2016-3
Financial liabilities
Other nonrecourse debt, net		138.0
Predecessor \| Fair Value, Measurements, Recurring \| Trust 2017-1
Financial liabilities
Other nonrecourse debt, net		213.0
Predecessor \| Fair Value, Measurements, Recurring \| Trust 2017-2
Financial liabilities
Other nonrecourse debt, net		365.0
Predecessor \| Fair Value, Measurements, Recurring \| Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net		37.0
Predecessor \| Fair Value, Measurements, Recurring \| 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, net		0.0
Warehouse facilities		0.0
Mortgage servicing rights financing liability		0.0
Excess spread financing		0.0
Derivative financial instruments		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 1 \| Participating interest financing
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 1 \| Trust 2016-2
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 1 \| Trust 2016-3
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 1 \| Trust 2017-1
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 1 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 1 \| Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| 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, net		855.0
Warehouse facilities		3,286.0
Mortgage servicing rights financing liability		0.0
Excess spread financing		0.0
Derivative financial instruments		5.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 2 \| Participating interest financing
Financial liabilities
Other nonrecourse debt, net		7,353.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 2 \| Trust 2016-2
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 2 \| Trust 2016-3
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 2 \| Trust 2017-1
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 2 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 2 \| Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| 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, net		0.0
Warehouse facilities		0.0
Mortgage servicing rights financing liability		10.0
Excess spread financing		996.0
Derivative financial instruments		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 3 \| Participating interest financing
Financial liabilities
Other nonrecourse debt, net		0.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 3 \| Trust 2016-2
Financial liabilities
Other nonrecourse debt, net		112.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 3 \| Trust 2016-3
Financial liabilities
Other nonrecourse debt, net		155.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 3 \| Trust 2017-1
Financial liabilities
Other nonrecourse debt, net		225.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 3 \| Trust 2017-2
Financial liabilities
Other nonrecourse debt, net		371.0
Predecessor \| Fair Value, Measurements, Recurring \| Level 3 \| Nonrecourse debt - legacy assets
Financial liabilities
Other nonrecourse debt, net		$ 36.0

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