Debt Schedule (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Debt Instrument
Long-term Debt, Excluding Current Maturities	$ 3,465.2	$ 3,430.4
Debt Instrument, Unamortized Discount (Premium), Noncurrent, Net	(131.3)	2.5
Debt Issuance Costs, Noncurrent, Net	(37.0)	(30.6)
Short-term debt	274.6	0.0
Debt Instrument, Unamortized Discount, Current	(0.2)	0.0
Debt Issuance Costs, Current, Net	0.2	0.0
Long-term Debt	3,739.8	3,430.4
Five-Year Term Loan Facility
Debt Instrument
Line of Credit Facility, Fair Value of Amount Outstanding	0.0	350.0
Notes Issued in 1998 with 2028 Maturity Date | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities	335.8	335.8
Notes Payable due 2032 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities	39.5	39.5
Notes Payable due 2042 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities	500.0	500.0
Notes Payable due 2025 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities	0.0	275.0
Short-term debt	275.0	0.0
Notes Payable due 2029 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities	400.0	400.0
Notes Payable due 2049 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities	450.0	450.0
Notes Payable due 2051 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities	600.0	600.0
Notes Payable due 2041 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities	400.0	0.0
Notes Payable due 2054 | Senior Notes
Debt Instrument
Long-term Debt, Excluding Current Maturities	400.0	0.0
Medium Term Notes Payable Due 2028 | Medium-Term Note
Debt Instrument
Long-term Debt, Excluding Current Maturities	18.5	18.5
Notes Issued in 1998 with 2038 Maturity Date | Junior Subordinated Debt
Debt Instrument
Long-term Debt, Excluding Current Maturities	189.7	189.7
Notes Payable due 2058 | Junior Subordinated Debt
Debt Instrument
Long-term Debt, Excluding Current Maturities	$ 300.0	$ 300.0