Senior Notes and Long-Term Debt - Senior Notes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Debt Instrument [Line Items]
Senior Notes	$ 2,769.7	$ 2,773.2
Senior Notes | Interest Rate Swaps
Debt Instrument [Line Items]
Change in unrealized gain (loss) on hedged item in fair value hedge	$ (224.2)	(219.1)
Fixed Rate Due May 2027
Debt Instrument [Line Items]
Interest rate	4.00%
Senior Notes	$ 998.3	997.6
Fixed Rate Due Aug. 2028
Debt Instrument [Line Items]
Interest rate	3.65%
Senior Notes	$ 479.6	483.3
Fixed Rate Due May 2029
Debt Instrument [Line Items]
Interest rate	3.15%
Senior Notes	$ 465.3	469.1
Fixed Rate Due May 2030
Debt Instrument [Line Items]
Interest rate	1.95%
Senior Notes	$ 826.5	$ 823.2