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Derivative Financial Instruments and Hedging Activities - Summary of Derivatives (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Derivative [Line Items]
Notional balance	$ 3,654.6		$ 3,654.6		$ 5,034.0
Derivatives, at fair value - See Note 15	72.3		72.3		28.1
Derivative liability, notional amount	3,282.1		3,282.1		4,186.6
Derivative liability, fair value	(52.9)		(52.9)		(9.1)
Gains (losses) on derivatives	(88.2)	$ (21.5)	(132.5)	$ (16.3)
Forward Sales Of Reverse Loans
Derivative [Line Items]
Derivative liability, notional amount	0.0		0.0		30.0
Derivative liability, fair value	0.0		0.0		(0.2)
Gains (losses) on derivatives	0.0	0.0	0.2	(0.5)
Forward loans IRLCs
Derivative [Line Items]
Notional balance	0.0		0.0		2,461.9
Derivatives, at fair value - See Note 15	0.0		0.0		16.5
Derivative liability, notional amount	995.1		995.1		0.0
Derivative liability, fair value	9.5		9.5		0.0
Gains (losses) on derivatives	(26.7)	(5.7)	(26.0)	12.1
Reverse loans IRLCs
Derivative [Line Items]
Notional balance	0.0		0.0		18.6
Derivatives, at fair value - See Note 15	0.0		0.0		0.8
Gains (losses) on derivatives	0.0	0.1	(0.8)	0.9
TBA forward MBS trades
Derivative [Line Items]
Notional balance	2,117.6		2,117.6		1,913.5
Derivatives, at fair value - See Note 15	57.1		57.1		8.4
Derivative liability, notional amount	317.0		317.0		2,171.6
Derivative liability, fair value	(5.0)		(5.0)		(6.6)
Interest Rate Swap
Derivative [Line Items]
Notional balance	237.0		237.0		590.0
Derivatives, at fair value - See Note 15	3.2		3.2		1.9
Derivative liability, notional amount	1,970.0		1,970.0		1,935.0
Derivative liability, fair value	(38.4)		(38.4)		(1.8)
TBA Forward Pipelines Trades
Derivative [Line Items]
Gains (losses) on derivatives			125.6	(53.2)
Interest Rate Swap Futures And TBA Forward MBS Trades
Derivative [Line Items]
Gains (losses) on derivatives	(180.8)	10.6	(242.9)	25.9
Forward LHFS Trades
Derivative [Line Items]
Gains (losses) on derivatives	0.0	1.2	0.0	(1.5)
Interest rate option contracts
Derivative [Line Items]
Notional balance	1,300.0		1,300.0		50.0
Derivatives, at fair value - See Note 15	12.0		12.0		0.5
Derivative liability, notional amount	0.0		0.0		50.0
Derivative liability, fair value	0.0		0.0		$ (0.5)
Future
Derivative [Line Items]
Gains (losses) on derivatives	6.6	0.0	$ 11.4	$ 0.0
TRA Trades And Interest Rate Futures
Derivative [Line Items]
Gains (losses) on derivatives	$ 112.7	$ (27.8)