Fair Value Accounting - Change in Level 3 Unobservable Inputs (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022 USD ($) percent	Dec. 31, 2021 USD ($) percent
Loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | $	$ 7.9	$ 45.5
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | $	292.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | $	(350.7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | $	38.5
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | $	0.0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | $	0.0
Interest Rate Lock Commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | $	(11.4)	9.4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | $	5,323.3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Issuances | $	(5,321.1)
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | $	(11.4)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | $	(23.0)
Servicing Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value | $	950.3	$ 698.0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases | $	204.1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales | $	0.0
Fair Value, Asset (Liability), Recurring Basis, Still Held, Unrealized Gain (Loss) | $	80.4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings | $	81.4
Realization of expected cash flows | $	$ (33.2)
Loans and Finance Receivables [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description	Discounted cash flow method	Discounted cash flow method
Loans and Finance Receivables [Member] | Level 3 [Member] | Scheduled Cash Collections [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description	Scheduled cash collections	Scheduled cash collections
Level 3 Fair Value Measurement Inputs	Probability of default	Probability of default
Loans and Finance Receivables [Member] | Level 3 [Member] | Proceeds from Non-Real Estate Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Valuation Processes, Description	Proceeds from non-real estate collateral	Proceeds from non-real estate collateral
Level 3 Fair Value Measurement Inputs	Loss given default	Loss given default
Option Adjusted Spread | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	623	735
Option Adjusted Spread | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	518	600
Option Adjusted Spread | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	408	553
Conditional Prepayment Rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	0.172	0.207
Conditional Prepayment Rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	13	15.2
Conditional Prepayment Rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	0.089	0.099
Servicing Fee Rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	50.0	50.0
Servicing Fee Rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	30.1	29.5
Servicing Fee Rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	25.0	25.0
Cost to Service | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	91	91
Cost to Service | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	86	86
Cost to Service | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	84	84
Servicing Fee Multiple | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Measurement Input	5.6	5.4
Servicing Fee Multiple | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Measurement Input	4.7	4.6
Servicing Fee Multiple | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Measurement Input	3.6	3.6
Pull-through Rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Measurement Input	1	1
Pull-through Rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Measurement Input	89	90
Pull-through Rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Measurement Input	0.73	0.75
Whole loan spread to TBA price in basis points | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Measurement Input	(2.0)	(2.9)
Whole loan spread to TBA price in basis points | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Measurement Input	(3.1)	(3.3)
Whole loan spread to TBA price in basis points | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Measurement Input	(4.2)	(3.7)
Recapture Rate | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	0.200	0.200
Recapture Rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	20	20
Recapture Rate | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing Asset, Measurement Input	0.200	0.200