Fair Value Measurements - Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Assets
Mortgage loans held for sale	$ 2,170.0	$ 1,631.0
Mortgage loans held for investment	118.0	119.0
Mortgage servicing rights	3,481.0	3,665.0
Liabilities
Mortgage servicing rights financing	34.0	32.0
Derivative instruments at fair value, less than	0.1	0.1
Recurring Fair Value Measurements
Assets
Mortgage loans held for sale	2,170.2	1,630.8
Mortgage loans held for investment	117.8	119.1
Mortgage servicing rights	3,481.0	3,665.4
Derivative financial instruments	72.0	49.0
Total assets	5,841.2	5,464.7
Liabilities
Mortgage servicing rights financing	33.7	31.7
Excess spread financing	1,309.2	1,184.4
Total liabilities	1,364.4	1,235.8
Recurring Fair Value Measurements \| IRLCs
Assets
Derivative financial instruments	68.9	47.6
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements \| Forward sales of MBS
Assets
Derivative financial instruments	1.3	0.1
Liabilities
Derivative financial instruments	21.3	19.3
Recurring Fair Value Measurements \| LPCs
Assets
Derivative financial instruments	2.0	1.7
Liabilities
Derivative financial instruments	0.2	0.4
Recurring Fair Value Measurements \| Eurodollar futures
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	0.0	0.0
Recurring Fair Value Measurements \| Level 1
Assets
Mortgage loans held for sale	0.0	0.0
Mortgage loans held for investment	0.0	0.0
Mortgage servicing rights	0.0	0.0
Derivative financial instruments	0.0	0.0
Total assets	0.0	0.0
Liabilities
Mortgage servicing rights financing	0.0	0.0
Excess spread financing	0.0	0.0
Total liabilities	0.0	0.0
Recurring Fair Value Measurements \| Level 1 \| IRLCs
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements \| Level 1 \| Forward sales of MBS
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	0.0	0.0
Recurring Fair Value Measurements \| Level 1 \| LPCs
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	0.0	0.0
Recurring Fair Value Measurements \| Level 1 \| Eurodollar futures
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	0.0	0.0
Recurring Fair Value Measurements \| Level 2
Assets
Mortgage loans held for sale	2,170.2	1,630.8
Mortgage loans held for investment	0.0	0.0
Mortgage servicing rights	0.0	0.0
Derivative financial instruments	72.0	49.0
Total assets	2,242.4	1,680.2
Liabilities
Mortgage servicing rights financing	0.0	0.0
Excess spread financing	0.0	0.0
Total liabilities	21.5	19.7
Recurring Fair Value Measurements \| Level 2 \| IRLCs
Assets
Derivative financial instruments	68.9	47.6
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements \| Level 2 \| Forward sales of MBS
Assets
Derivative financial instruments	1.3	0.1
Liabilities
Derivative financial instruments	21.3	19.3
Recurring Fair Value Measurements \| Level 2 \| LPCs
Assets
Derivative financial instruments	2.0	1.7
Liabilities
Derivative financial instruments	0.2	0.4
Recurring Fair Value Measurements \| Level 2 \| Eurodollar futures
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	0.0	0.0
Recurring Fair Value Measurements \| Level 3
Assets
Mortgage loans held for sale	0.0	0.0
Mortgage loans held for investment	117.8	119.1
Mortgage servicing rights	3,481.0	3,665.4
Derivative financial instruments	0.0	0.0
Total assets	3,598.8	3,784.5
Liabilities
Mortgage servicing rights financing	33.7	31.7
Excess spread financing	1,309.2	1,184.4
Total liabilities	1,342.9	1,216.1
Recurring Fair Value Measurements \| Level 3 \| IRLCs
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements \| Level 3 \| Forward sales of MBS
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	0.0	0.0
Recurring Fair Value Measurements \| Level 3 \| LPCs
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	0.0	0.0
Recurring Fair Value Measurements \| Level 3 \| Eurodollar futures
Assets
Derivative financial instruments	0.0	0.0
Liabilities
Derivative financial instruments	$ 0.0	$ 0.0
Predecessor
Liabilities
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