Derivatives and Financial Instruments - Recorded Amounts and Estimated Fair Values (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Derivative [Line Items]
Total debt	$ 1,993.6	$ 2,317.3
Recorded Amount
Derivative [Line Items]
Variable rate debt	1,193.8	1,520.0
Fixed rate debt	819.3	819.3
Total debt	2,013.1	2,339.3
Fair Value
Derivative [Line Items]
Variable rate debt	1,193.8	1,520.0
Fixed rate debt	777.7	789.3
Total debt	$ 1,971.5	$ 2,309.3