Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 692.5	$ 732.4
Other comprehensive income, net of tax	18.0	9.1
Ending balance	708.2	735.0
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(21.4)	(19.8)
Less: income tax benefit (expense)	(0.3)	(0.3)
Other comprehensive income, net of tax	0.9	0.7
Ending balance	(20.5)	(19.1)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI		0.1
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI	1.2	0.9
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	17.7	1.1
Unrealized gain on securities	42.3	13.9
Less: income tax expense	(10.0)	(3.3)
Net unrealized gain on available for sale securities, cash flow hedges and fair value hedges	32.3	10.6
Reclassification from AOCI	(19.9)	(2.7)
Less: income tax benefit (expense)	4.7	0.6
Net gain reclassified from AOCI to Net income	(15.2)	(2.1)
Other comprehensive income, net of tax	17.1	8.5
Ending balance	34.8	9.6
AOCI, Accumulated Foreign Currency Adjustment Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income, net of tax		(0.1)
Ending balance		(0.1)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(3.7)	(18.7)
Other comprehensive income, net of tax	18.0	9.1
Ending balance	$ 14.3	$ (9.6)