Fair Value Measurements - Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets
Mortgage loans held for sale	$ 1,681.0
Mortgage loans held for investment(1)	122.0
Mortgage servicing rights	3,485.0
Liabilities
Mortgage servicing rights financing	26.0	$ 10.0
Derivative instruments at fair value, less than	0.1
Recurring Fair Value Measurements
Assets
Mortgage loans held for sale	1,681.1
Mortgage loans held for investment(1)	121.6
Mortgage servicing rights	3,485.4
Derivative financial instruments	72.0
Total assets	5,359.8
Liabilities
Mortgage servicing rights financing	26.3
Excess spread financing	1,096.5
Total liabilities	1,124.9
Recurring Fair Value Measurements | IRLCs
Assets
Derivative financial instruments	57.8
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Forward sales of MBS
Assets
Derivative financial instruments	12.2
Liabilities
Derivative financial instruments	0.5
Recurring Fair Value Measurements | LPCs
Assets
Derivative financial instruments	1.7
Liabilities
Derivative financial instruments	1.5
Recurring Fair Value Measurements | Eurodollar futures
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Treasury futures(2)
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.1
Recurring Fair Value Measurements | Level 1
Assets
Mortgage loans held for sale	0.0
Mortgage loans held for investment(1)	0.0
Mortgage servicing rights	0.0
Derivative financial instruments	0.0
Total assets	0.0
Liabilities
Mortgage servicing rights financing	0.0
Excess spread financing	0.0
Total liabilities	0.0
Recurring Fair Value Measurements | Level 1 | IRLCs
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 1 | Forward sales of MBS
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 1 | LPCs
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 1 | Eurodollar futures
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 1 | Treasury futures(2)
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 2
Assets
Mortgage loans held for sale	1,681.1
Mortgage loans held for investment(1)	0.0
Mortgage servicing rights	0.0
Derivative financial instruments	72.0
Total assets	1,752.8
Liabilities
Mortgage servicing rights financing	0.0
Excess spread financing	0.0
Total liabilities	2.1
Recurring Fair Value Measurements | Level 2 | IRLCs
Assets
Derivative financial instruments	57.8
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 2 | Forward sales of MBS
Assets
Derivative financial instruments	12.2
Liabilities
Derivative financial instruments	0.5
Recurring Fair Value Measurements | Level 2 | LPCs
Assets
Derivative financial instruments	1.7
Liabilities
Derivative financial instruments	1.5
Recurring Fair Value Measurements | Level 2 | Eurodollar futures
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 2 | Treasury futures(2)
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.1
Recurring Fair Value Measurements | Level 3
Assets
Mortgage loans held for sale	0.0
Mortgage loans held for investment(1)	121.6
Mortgage servicing rights	3,485.4
Derivative financial instruments	0.0
Total assets	3,607.0
Liabilities
Mortgage servicing rights financing	26.3
Excess spread financing	1,096.5
Total liabilities	1,122.8
Recurring Fair Value Measurements | Level 3 | IRLCs
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 3 | Forward sales of MBS
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 3 | LPCs
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 3 | Eurodollar futures
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	0.0
Recurring Fair Value Measurements | Level 3 | Treasury futures(2)
Assets
Derivative financial instruments	0.0
Liabilities
Derivative financial instruments	$ 0.0
Predecessor
Assets
Mortgage loans held for sale		1,891.0
Mortgage loans held for investment(1)		139.0
Mortgage servicing rights		2,937.0
Liabilities
Mortgage servicing rights financing		10.0
Derivative instruments at fair value, less than		0.1
Predecessor | Recurring Fair Value Measurements
Assets
Mortgage loans held for sale		1,890.8
Mortgage loans held for investment(1)		139.0
Mortgage servicing rights		2,937.4
Derivative financial instruments		65.0
Total assets		4,892.7
Liabilities
Mortgage servicing rights financing		9.5
Excess spread financing		996.5
Total liabilities		1,010.8
Predecessor | Recurring Fair Value Measurements | IRLCs
Assets
Derivative financial instruments		59.3
Predecessor | Recurring Fair Value Measurements | Forward sales of MBS
Assets
Derivative financial instruments		2.4
Liabilities
Derivative financial instruments		2.8
Predecessor | Recurring Fair Value Measurements | LPCs
Assets
Derivative financial instruments		0.9
Liabilities
Derivative financial instruments		0.6
Predecessor | Recurring Fair Value Measurements | Eurodollar futures
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Treasury futures(2)
Assets
Derivative financial instruments		1.9
Liabilities
Derivative financial instruments		1.4
Predecessor | Recurring Fair Value Measurements | Level 1
Assets
Mortgage loans held for sale		0.0
Mortgage loans held for investment(1)		0.0
Mortgage servicing rights		0.0
Derivative financial instruments		0.0
Total assets		0.0
Liabilities
Mortgage servicing rights financing		0.0
Excess spread financing		0.0
Total liabilities		0.0
Predecessor | Recurring Fair Value Measurements | Level 1 | IRLCs
Assets
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 1 | Forward sales of MBS
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 1 | LPCs
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 1 | Eurodollar futures
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 1 | Treasury futures(2)
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 2
Assets
Mortgage loans held for sale		1,890.8
Mortgage loans held for investment(1)		0.0
Mortgage servicing rights		0.0
Derivative financial instruments		65.0
Total assets		1,955.3
Liabilities
Mortgage servicing rights financing		0.0
Excess spread financing		0.0
Total liabilities		4.8
Predecessor | Recurring Fair Value Measurements | Level 2 | IRLCs
Assets
Derivative financial instruments		59.3
Predecessor | Recurring Fair Value Measurements | Level 2 | Forward sales of MBS
Assets
Derivative financial instruments		2.4
Liabilities
Derivative financial instruments		2.8
Predecessor | Recurring Fair Value Measurements | Level 2 | LPCs
Assets
Derivative financial instruments		0.9
Liabilities
Derivative financial instruments		0.6
Predecessor | Recurring Fair Value Measurements | Level 2 | Eurodollar futures
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 2 | Treasury futures(2)
Assets
Derivative financial instruments		1.9
Liabilities
Derivative financial instruments		1.4
Predecessor | Recurring Fair Value Measurements | Level 3
Assets
Mortgage loans held for sale		0.0
Mortgage loans held for investment(1)		139.0
Mortgage servicing rights		2,937.4
Derivative financial instruments		0.0
Total assets		2,937.4
Liabilities
Mortgage servicing rights financing		9.5
Excess spread financing		996.5
Total liabilities		1,006.0
Predecessor | Recurring Fair Value Measurements | Level 3 | IRLCs
Assets
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 3 | Forward sales of MBS
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 3 | LPCs
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 3 | Eurodollar futures
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		0.0
Predecessor | Recurring Fair Value Measurements | Level 3 | Treasury futures(2)
Assets
Derivative financial instruments		0.0
Liabilities
Derivative financial instruments		$ 0.0