Fair Value Measurements - Measured on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Assets
Mortgage loans held for sale	$ 3,922.0	$ 4,077.0
Mortgage servicing rights	3,109.0	3,496.0
Derivative financial instruments	294.0	153.0
Liabilities
Mortgage servicing rights financing	43.0	37.0
Recurring Fair Value Measurements
Assets
Mortgage loans held for sale	3,922.0	4,077.0
Mortgage servicing rights	3,109.0	3,496.0
Derivative financial instruments	294.0	153.0
Total assets	7,325.0	7,727.0
Liabilities
Mortgage servicing rights financing	43.0	37.0
Excess spread financing	1,242.0	1,311.0
Total liabilities	1,508.0	1,363.0
Recurring Fair Value Measurements \| IRLCs
Assets
Derivative financial instruments	263.0	135.0
Recurring Fair Value Measurements \| Forward MBS trades
Assets
Derivative financial instruments	6.0	7.0
Liabilities
Derivative financial instruments	223.0	12.0
Recurring Fair Value Measurements \| LPCs
Assets
Derivative financial instruments	25.0	12.0
Liabilities
Derivative financial instruments		3.0
Recurring Fair Value Measurements \| Level 1
Assets
Mortgage loans held for sale	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
Recurring Fair Value Measurements \| Level 1 \| Forward MBS trades
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
Recurring Fair Value Measurements \| Level 2
Assets
Mortgage loans held for sale	3,922.0	4,077.0
Mortgage servicing rights	0.0	0.0
Derivative financial instruments	294.0	153.0
Total assets	4,216.0	4,231.0
Liabilities
Mortgage servicing rights financing	0.0	0.0
Excess spread financing	0.0	0.0
Total liabilities	223.0	15.0
Recurring Fair Value Measurements \| Level 2 \| IRLCs
Assets
Derivative financial instruments	263.0	135.0
Recurring Fair Value Measurements \| Level 2 \| Forward MBS trades
Assets
Derivative financial instruments	6.0	7.0
Liabilities
Derivative financial instruments	223.0	12.0
Recurring Fair Value Measurements \| Level 2 \| LPCs
Assets
Derivative financial instruments	25.0	12.0
Liabilities
Derivative financial instruments		3.0
Recurring Fair Value Measurements \| Level 3
Assets
Mortgage loans held for sale	0.0	0.0
Mortgage servicing rights	3,109.0	3,496.0
Derivative financial instruments	0.0	0.0
Total assets	3,109.0	3,496.0
Liabilities
Mortgage servicing rights financing	43.0	37.0
Excess spread financing	1,242.0	1,311.0
Total liabilities	1,285.0	1,348.0
Recurring Fair Value Measurements \| Level 3 \| IRLCs
Assets
Derivative financial instruments	0.0	0.0
Recurring Fair Value Measurements \| Level 3 \| Forward MBS trades
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

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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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- Definition

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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Fair value of financial and nonfinancial obligations.

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Fair value portion of mortgage loans held-for-sale.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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