Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive (Loss) Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 732.4	$ 733.9	$ 740.4
Other comprehensive income, net of tax	15.0	19.9	10.2
Ending balance	692.5	732.4	733.9
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(19.8)	(33.2)	(35.6)
Less: income tax (expense) benefit	(0.9)	(1.2)	(1.4)
Net loss (gain) reclassified from AOCI to Net (loss) income	3.0	3.9	4.7
Translation impact on Canadian pension plan AOCI balance		(0.1)	(0.1)
Other comprehensive income, net of tax	(1.6)	13.4	2.4
Ending balance	(21.4)	(19.8)	(33.2)
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Unrealized gain (loss) on securities	8.0	0.4	(0.4)
Less: income tax (expense) benefit	(1.9)	(0.1)	0.1
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges	6.1	0.3	(0.3)
Reclassification from AOCI	0.4	0.4	0.5
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Unrealized gain (loss) on securities	(14.0)	12.3	(2.5)
Less: income tax (expense) benefit	3.3	(3.0)	0.6
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges	(10.7)	9.3	(1.9)
Reclassification from AOCI	3.5	4.7	5.6
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1.1	(5.6)	(13.4)
Unrealized gain (loss) on securities	63.6	(9.4)	(9.5)
Less: income tax (expense) benefit	(15.0)	2.3	2.3
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges	48.6	(7.1)	(7.2)
Reclassification from AOCI	(41.9)	17.4	19.7
Reclassification due to forecasted transactions no longer probable of occurring		0.8
Less: income tax (expense) benefit	9.9	(4.4)	(4.7)
Net loss (gain) reclassified from AOCI to Net (loss) income	(32.0)	13.8	15.0
Other comprehensive income, net of tax	16.6	6.7	7.8
Ending balance	17.7	1.1	(5.6)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0.3	0.3
Unrealized gain (loss) on securities		1.3	4.4
Less: income tax (expense) benefit		(0.7)	(1.1)
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges		0.6	3.3
Reclassification from AOCI		(2.0)	(4.4)
Less: income tax (expense) benefit		1.1	1.1
Net loss (gain) reclassified from AOCI to Net (loss) income		(0.9)	(3.3)
Other comprehensive income, net of tax		(0.3)
Ending balance			0.3
AOCI, Excluded Component of Derivative Qualifying as Fair Value Hedge Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Unrealized gain (loss) on securities		(1.0)
Less: income tax (expense) benefit		0.2
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges		(0.8)
Reclassification from AOCI		0.4
Reclassification due to cancellation of firm commitment		0.6
Less: income tax (expense) benefit		(0.2)
Net loss (gain) reclassified from AOCI to Net (loss) income		0.8
AOCI, Accumulated Foreign Currency Adjustment Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(0.1)	(0.1)
Other comprehensive income, net of tax		0.1
Ending balance			(0.1)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(18.7)	(38.6)	(48.8)
Other comprehensive income, net of tax	15.0	19.9	10.2
Ending balance	$ (3.7)	$ (18.7)	$ (38.6)