Components of Pension Expense (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 107.6	$ 94.0	$ 148.5
Interest on projected benefit obligation	135.0	127.5	84.9
Expected return on assets	$ (243.7)	$ (230.3)	$ (215.1)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Excluding Service Cost, Statement of Income or Comprehensive Income [Extensible Enumeration]	Costs and Expenses	Costs and Expenses	Costs and Expenses
Amortization of prior service costs	$ 1.4	$ 1.4	$ 0.7
Recognized actuarial loss	7.2	4.7	28.9
Net pension expense (gain)	$ 7.5	$ (2.7)	$ 47.9