Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,735.2	$ 1,857.8
Other comprehensive income (loss) before reclassifications	(260.7)	(18.5)
Amounts reclassified from accumulated other comprehensive loss	27.4	(16.9)
Net current-period other comprehensive loss	(233.3)	(35.4)
Ending Balance	1,460.7	1,897.9
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	(0.4)	2.5
Amounts reclassified from accumulated other comprehensive loss	31.8	0.0
Net current-period other comprehensive loss	31.4	2.5
Ending Balance	(3.9)	(35.4)
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	(260.3)	(22.5)
Amounts reclassified from accumulated other comprehensive loss	(4.4)	(16.9)
Net current-period other comprehensive loss	(264.7)	(39.4)
Ending Balance	(245.0)	65.7
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	1.5
Amounts reclassified from accumulated other comprehensive loss	0.0	0.0
Net current-period other comprehensive loss	0.0	1.5
Ending Balance	(7.1)	(7.1)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(22.7)	58.6
Ending Balance	$ (256.0)	$ 23.2