Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Derivative, Notional Amount	$ 31.9	$ 34.2
Derivative Asset	0.3	0.1
Derivative Liability	0.0	0.1
Commercial Paper	0.0	30.0
Other Assets, Fair Value Disclosure	1.5	1.5
Long-term Debt, Fair Value	$ 983.1	$ 954.8