Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,735.2	$ 1,857.8
Other comprehensive income (loss) before reclassifications	(135.1)	(51.2)
Amounts reclassified from accumulated other comprehensive loss	22.9	(3.2)
Net current-period other comprehensive loss	(112.2)	(54.4)
Ending Balance	1,610.8	1,821.0
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(35.3)	(37.9)
Other comprehensive income (loss) before reclassifications	4.1	(0.9)
Amounts reclassified from accumulated other comprehensive loss	27.3	0.0
Net current-period other comprehensive loss	31.4	(0.9)
Ending Balance	(3.9)	(38.8)
Unrealized Holding Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	19.7	105.1
Other comprehensive income (loss) before reclassifications	(139.2)	(50.3)
Amounts reclassified from accumulated other comprehensive loss	(4.4)	(3.2)
Net current-period other comprehensive loss	(143.6)	(53.5)
Ending Balance	(123.9)	51.6
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(7.1)	(8.6)
Other comprehensive income (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	(7.1)	(8.6)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(22.7)	58.6
Ending Balance	$ (134.9)	$ 4.2