Fair Value Measurements - Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
ASSETS
Mortgage loans held for sale at fair value	$ 4,077.0	$ 1,631.0
Mortgage loans held for investment at fair value	0.0	119.0
Mortgage servicing rights	3,496.0	3,665.0
Derivative financial instruments	153.0	49.0
LIABILITIES
Derivative instrument, fair value (less than)	0.1	0.1
Fair Value, Measurements, Recurring
ASSETS
Mortgage loans held for sale at fair value	4,077.0	1,630.8
Mortgage loans held for investment at fair value	0.0	119.1
Mortgage servicing rights	3,496.4	3,665.4
Derivative financial instruments	153.0	49.0
Total assets	7,726.8	5,464.7
LIABILITIES
Mortgage servicing rights financing liability	37.4	31.7
Excess spread financing	1,310.8	1,184.4
Total liabilities	1,363.1	1,235.8
Fair Value, Measurements, Recurring \| Level 1
ASSETS
Mortgage loans held for sale at fair value	0.0	0.0
Mortgage loans held for investment at fair value	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 liability	0.0	0.0
Excess spread financing	0.0	0.0
Total liabilities	0.0	0.0
Fair Value, Measurements, Recurring \| Level 2
ASSETS
Mortgage loans held for sale at fair value	4,077.0	1,630.8
Mortgage loans held for investment at fair value	0.0	0.0
Mortgage servicing rights	0.0	0.0
Derivative financial instruments	153.0	49.0
Total assets	4,230.4	1,680.2
LIABILITIES
Mortgage servicing rights financing liability	0.0	0.0
Excess spread financing	0.0	0.0
Total liabilities	14.9	19.7
Fair Value, Measurements, Recurring \| Level 3
ASSETS
Mortgage loans held for sale at fair value	0.0	0.0
Mortgage loans held for investment at fair value	0.0	119.1
Mortgage servicing rights	3,496.4	3,665.4
Derivative financial instruments	0.0	0.0
Total assets	3,496.4	3,784.5
LIABILITIES
Mortgage servicing rights financing liability	37.4	31.7
Excess spread financing	1,310.8	1,184.4
Total liabilities	1,348.2	1,216.1
IRLCs \| Fair Value, Measurements, Recurring
ASSETS
Derivative financial instruments	134.7	47.6
LIABILITIES
Derivative financial instruments	0.0
IRLCs \| Fair Value, Measurements, Recurring \| Level 1
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	0.0
IRLCs \| Fair Value, Measurements, Recurring \| Level 2
ASSETS
Derivative financial instruments	134.7	47.6
LIABILITIES
Derivative financial instruments	0.0
IRLCs \| Fair Value, Measurements, Recurring \| Level 3
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	0.0
Forward MBS trades \| Fair Value, Measurements, Recurring
ASSETS
Derivative financial instruments	6.5	0.1
LIABILITIES
Derivative financial instruments	12.3	19.3
Forward MBS trades \| Fair Value, Measurements, Recurring \| Level 1
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	0.0	0.0
Forward MBS trades \| Fair Value, Measurements, Recurring \| Level 2
ASSETS
Derivative financial instruments	6.5	0.1
LIABILITIES
Derivative financial instruments	12.3	19.3
Forward MBS trades \| Fair Value, Measurements, Recurring \| Level 3
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	0.0	0.0
LPCs \| Fair Value, Measurements, Recurring
ASSETS
Derivative financial instruments	12.2	1.7
LIABILITIES
Derivative financial instruments	2.6	0.4
LPCs \| Fair Value, Measurements, Recurring \| Level 1
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	0.0	0.0
LPCs \| Fair Value, Measurements, Recurring \| Level 2
ASSETS
Derivative financial instruments	12.2	1.7
LIABILITIES
Derivative financial instruments	2.6	0.4
LPCs \| Fair Value, Measurements, Recurring \| Level 3
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	0.0	0.0
Eurodollar futures \| Fair Value, Measurements, Recurring
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	0.0	0.0
Eurodollar futures \| Fair Value, Measurements, Recurring \| Level 1
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	0.0	0.0
Eurodollar futures \| Fair Value, Measurements, Recurring \| Level 2
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	0.0	0.0
Eurodollar futures \| Fair Value, Measurements, Recurring \| Level 3
ASSETS
Derivative financial instruments	0.0	0.0
LIABILITIES
Derivative financial instruments	$ 0.0	$ 0.0

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Mortgage loans held for investment, subject to nonrecourse debt - Legacy Assets, net of allowance for loan losses, respectively

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Mortgage Servicing Rights Liability Resulting from Sale or Securitization of Servicer Advances, Rights not Accounted for as a Sale

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Aggregate net fair value of all derivative instruments designated as hedging instruments. Includes instruments designated as cash flow hedges, fair value hedges, and hedges of net investments in foreign operations.

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