Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,857.8	$ 1,763.7
Other comprehensive loss before reclassifications	(51.2)	(105.1)
Amounts reclassified from accumulated other comprehensive loss	(3.2)	(5.3)
Net current-period other comprehensive loss	(54.4)	(110.4)
Ending Balance	1,821.0	1,613.5
Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		(2.2)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(37.9)	(22.6)
Other comprehensive loss before reclassifications	(0.9)	(3.4)
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0
Net current-period other comprehensive loss	(0.9)	(3.4)
Ending Balance	(38.8)	(26.0)
Foreign Currency Translation Adjustments \| Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		0.0
Unrealized Holding Gains on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	105.1	33.5
Other comprehensive loss before reclassifications	(50.3)	(101.7)
Amounts reclassified from accumulated other comprehensive loss	(3.2)	(5.3)
Net current-period other comprehensive loss	(53.5)	(107.0)
Ending Balance	51.6	(67.8)
Unrealized Holding Gains on Securities \| Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		5.7
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(8.6)	(8.1)
Other comprehensive loss before reclassifications	0.0	0.0
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0
Net current-period other comprehensive loss	0.0	0.0
Ending Balance	(8.6)	(8.1)
Defined Benefit Pension Plans \| Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		0.0
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	58.6	2.8
Ending Balance	$ 4.2	(101.9)
Accumulated Other Comprehensive Income (Loss) \| Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance		$ 5.7

Other Comprehensive Income (Loss), Net of Tax, Including Cumulative Effect of Adoption

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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