Accumulated Other Comprehensive (Loss) Income - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended						6 Months Ended
		Jun. 30, 2022		Mar. 31, 2022	Jun. 30, 2021		Mar. 31, 2021	Jun. 30, 2022		Jun. 30, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 708.2		$ 692.5	$ 735.0		$ 732.4	$ 692.5		$ 732.4
Other comprehensive (loss) income, net of tax		(35.6)		18.0	15.9		9.1	(17.6)		25.0
Ending balance		650.0		708.2	720.7		735.0	650.0		720.7
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(20.5)		(21.4)	(19.1)		(19.8)	(21.4)		(19.8)
Less: income tax benefit (expense)		(0.4)			(0.2)			(0.7)		(0.5)
Other comprehensive (loss) income, net of tax		0.9			0.7			1.8		1.4
Ending balance		(19.6)		(20.5)	(18.4)		(19.1)	(19.6)		(18.4)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI	[1]				0.1					0.2
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI	[1]	1.3			0.8			2.5		1.7
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		34.8		17.7	9.6		1.1	17.7		1.1
Unrealized gain on securities		(50.7)			28.4			(8.4)		42.3
Less: income tax expense		12.0			(6.7)			2.0		(10.0)
Net unrealized gain on available for sale securities, cash flow hedges and fair value hedges		(38.7)			21.7			(6.4)		32.3
Reclassification from AOCI		2.9			(8.7)			(17.0)		(11.4)
Less: income tax benefit (expense)	[2]	(0.7)			2.2			4.0		2.8
Net loss (gain) reclassified from AOCI to Net loss		2.2			(6.5)			(13.0)		(8.6)
Other comprehensive (loss) income, net of tax		(36.5)			15.2			(19.4)		23.7
Ending balance		(1.7)	[3]	34.8	24.8	[3]	9.6	(1.7)	[3]	24.8	[3]
AOCI, Accumulated Foreign Currency Adjustment Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance					(0.1)
Other comprehensive (loss) income, net of tax										(0.1)
Ending balance					(0.1)		(0.1)			(0.1)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		14.3		(3.7)	(9.6)		(18.7)	(3.7)		(18.7)
Other comprehensive (loss) income, net of tax		(35.6)		18.0	15.9		9.1
Ending balance		$ (21.3)		$ 14.3	$ 6.3		$ (9.6)	$ (21.3)		$ 6.3

[1] Amounts amortized out of AOCI relating to Salaried VEBA adjustments were included within Other expense, net, as a component of Net periodic postretirement benefit cost relating to Salaried VEBA

[2] Income tax amounts reclassified out of AOCI were included as a component of Income tax benefit.

[3] As of June 30, 2022, we estimate a net mark-to-market loss before tax of $6.0 million in AOCI will be reclassified into Net loss upon settlement within the next 12 months.