Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 1,735.2	$ 1,857.8
Other comprehensive (loss) income before reclassifications	(348.6)	(73.3)
Amounts reclassified from accumulated other comprehensive income	66.2	(8.0)
Net current-period other comprehensive income (loss)	(282.4)	(81.3)
Ending Balance	1,232.9	1,735.2
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(35.3)	(37.9)
Other comprehensive (loss) income before reclassifications	(0.7)	2.6
Amounts reclassified from accumulated other comprehensive income	31.8	0.0
Net current-period other comprehensive income (loss)	31.1	2.6
Ending Balance	(4.2)	(35.3)
Unrealized Holding Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	19.7	105.1
Other comprehensive (loss) income before reclassifications	(347.2)	(77.4)
Amounts reclassified from accumulated other comprehensive income	34.4	(8.0)
Net current-period other comprehensive income (loss)	(312.8)	(85.4)
Ending Balance	(293.1)	19.7
Defined Benefit Pension Plans
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(7.1)	(8.6)
Other comprehensive (loss) income before reclassifications	(0.7)	1.5
Amounts reclassified from accumulated other comprehensive income	0.0	0.0
Net current-period other comprehensive income (loss)	(0.7)	1.5
Ending Balance	(7.8)	(7.1)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(22.7)	58.6
Ending Balance	$ (305.1)	$ (22.7)