Derivative Financial Instruments and Hedging Activities - Summary of Derivatives (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Derivative [Line Items]
Notional balance	$ 4,122.8		$ 4,122.8		$ 1,916.6
Derivatives, at fair value - See Note 15	18.3		18.3		15.4
Derivative liability, notional amount	3,773.8		3,773.8		2,975.6
Derivative liability, fair value	(26.8)		(26.8)		(27.6)
Gains (losses) on derivatives	(21.5)	$ 19.4	(16.3)	$ (76.7)
Forward Sales Of Reverse Loans
Derivative [Line Items]
Notional balance	0.0		0.0		60.0
Derivatives, at fair value - See Note 15	0.0		0.0		0.4
Derivative liability, notional amount	30.0		30.0		0.0
Derivative liability, fair value	(0.1)		(0.1)		0.0
Gains (losses) on derivatives	0.0	0.0	(0.5)	0.1
Forward loans IRLCs
Derivative [Line Items]
Notional balance	2,367.7		2,367.7		0.0
Derivatives, at fair value - See Note 15	11.4		11.4		0.0
Derivative liability, notional amount	0.0		0.0		1,311.6
Derivative liability, fair value	0.0		0.0		0.7
Gains (losses) on derivatives	(5.7)	1.1	12.1	(0.4)
Reverse loans IRLCs
Derivative [Line Items]
Notional balance	33.9		33.9		25.6
Derivatives, at fair value - See Note 15	1.2		1.2		0.2
Gains (losses) on derivatives	0.1	(0.1)	0.9	0.0
TBA forward MBS trades
Derivative [Line Items]
Notional balance	1,670.9		1,670.9		1,391.1
Derivatives, at fair value - See Note 15	5.7		5.7		10.0
Derivative liability, notional amount	1,968.8		1,968.8		789.0
Derivative liability, fair value	(8.7)		(8.7)		(5.0)
Interest Rate Swap
Derivative [Line Items]
Notional balance	50.0		50.0		225.0
Derivatives, at fair value - See Note 15	0.0		0.0		3.2
Derivative liability, notional amount	1,675.0		1,675.0		875.0
Derivative liability, fair value	(18.0)		(18.0)		(21.9)
TBA Forward Pipelines Trades
Derivative [Line Items]
Gains (losses) on derivatives	(27.8)	(36.5)	(53.2)	(26.8)
Interest Rate Swap Futures And TBA Forward MBS Trades
Derivative [Line Items]
Gains (losses) on derivatives	10.6	54.3	25.9	(50.0)
Forward Trades
Derivative [Line Items]
Notional balance	0.4		0.4		215.0
Derivatives, at fair value - See Note 15	0.0		0.0		1.5
Forward LHFS Trades
Derivative [Line Items]
Gains (losses) on derivatives	1.2	$ 0.5	(1.5)	$ 0.5
Interest rate option contracts
Derivative [Line Items]
Derivative liability, notional amount	100.0		100.0		0.0
Derivative liability, fair value	$ 0.0		$ 0.0		$ 0.0

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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