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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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Derivative [Line Items]
Notional balance	$ 3,171.1		$ 3,171.1		$ 3,978.7
Derivatives, at fair value	10.1		10.1		21.6
Derivative liability, notional amount	1,764.3		1,764.3		920.2
Derivative liability, fair value	(13.9)		(13.9)		(7.0)
Gains (losses) on derivatives	19.4	$ (37.3)	(76.7)	$ (81.3)
Forward Sales Of Reverse Loans
Derivative [Line Items]
Notional balance	20.0		20.0		0.0
Derivatives, at fair value	0.0		0.0		0.0
Derivative liability, notional amount	20.0		20.0		50.0
Derivative liability, fair value	0.0		0.0		(0.1)
Gains (losses) on derivatives	0.0	(0.2)	0.1	(0.2)
Forward loans IRLCs
Derivative [Line Items]
Notional balance	1,673.4		1,673.4		592.5
Derivatives, at fair value	4.6		4.6		5.1
Gains (losses) on derivatives	1.1	(2.7)	(0.4)	(0.2)
Reverse loans IRLCs
Derivative [Line Items]
Notional balance	26.9		26.9		22.1
Derivatives, at fair value	0.6		0.6		0.6
Gains (losses) on derivatives	(0.1)	0.1	0.0	(0.2)
TBA forward MBS trades
Derivative [Line Items]
Notional balance	1,205.8		1,205.8		1,818.6
Derivatives, at fair value	3.9		3.9		10.1
Derivative liability, notional amount	979.3		979.3		854.9
Derivative liability, fair value	(5.3)		(5.3)		(6.8)
Interest Rate Swap
Derivative [Line Items]
Notional balance	75.0		75.0		790.0
Derivatives, at fair value	0.4		0.4		3.9
Derivative liability, notional amount	675.0		675.0		0.0
Derivative liability, fair value	(8.6)		(8.6)		0.0
Interest rate option contracts
Derivative [Line Items]
Notional balance	0.0		0.0		750.0
Derivatives, at fair value	0.0		0.0		1.9
TBA Forward Pipelines Trades
Derivative [Line Items]
Gains (losses) on derivatives	(36.5)	33.1	(26.8)	37.9
Interest Rate Swap Futures And TBA Forward MBS Trades
Derivative [Line Items]
Gains (losses) on derivatives	54.3	(68.6)	(50.0)	(119.7)
Other
Derivative [Line Items]
Derivative liability, notional amount	0.0		0.0		15.3
Derivative liability, fair value	0.0		0.0		(0.1)
Other Derivatives
Derivative [Line Items]
Gains (losses) on derivatives	0.0	(0.1)	0.0	0.2
Forward Trades
Derivative [Line Items]
Notional balance	170.0		170.0		5.5
Derivatives, at fair value	0.5		0.5		0.0
Derivative liability, notional amount	90.0		90.0		0.0
Derivative liability, fair value	0.0		0.0		$ 0.0
Forward LHFS Trades
Derivative [Line Items]
Gains (losses) on derivatives	$ 0.5	$ 1.0	$ 0.5	$ 1.0