Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 732.4	$ 733.9
Other comprehensive income (loss), net of tax	9.1	(15.5)
Ending balance	735.0	721.1
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(19.8)	(33.2)
Less: income tax (expense) benefit	(0.3)	(0.3)
Net loss (gain) reclassified from AOCI to Net income	0.7	1.0
Translation impact on Canadian pension plan AOCI balance		0.1
Other comprehensive income (loss), net of tax	0.7	1.1
Ending balance	(19.1)	(32.1)
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	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	0.9	1.2
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		0.3
Unrealized gain (loss) on securities		1.3
Less: income tax benefit (expense)		(0.3)
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges		1.0
Reclassification from AOCI		(1.5)
Less: income tax (expense) benefit		0.3
Net loss (gain) reclassified from AOCI to Net income		(1.2)
Other comprehensive income (loss), net of tax		(0.2)
Ending balance		0.1
AOCI, Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	1.1	(5.6)
Unrealized gain (loss) on securities	13.9	(27.9)
Less: income tax benefit (expense)	(3.3)	6.8
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges	10.6	(21.1)
Reclassification from AOCI	(2.7)	7.0
Less: income tax (expense) benefit	0.6	(1.8)
Net loss (gain) reclassified from AOCI to Net income	(2.1)	5.2
Other comprehensive income (loss), net of tax	8.5	(15.9)
Ending balance	9.6	(21.5)
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		(0.8)
Less: income tax benefit (expense)		0.2
Net unrealized gain (loss) on available for sale securities, cash flow hedges and fair value hedges		(0.6)
Reclassification from AOCI		0.2
Less: income tax (expense) benefit		(0.1)
Net loss (gain) reclassified from AOCI to Net income		0.1
Other comprehensive income (loss), net of tax		(0.5)
Ending balance		(0.5)
AOCI, Accumulated Foreign Currency Adjustment Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(0.1)
Other comprehensive income (loss), net of tax	(0.1)
Ending balance	(0.1)	(0.1)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(18.7)	(38.6)
Other comprehensive income (loss), net of tax	9.1	(15.5)
Ending balance	$ (9.6)	$ (54.1)