Defined Benefit and Postretirement Benefits (Components Of Net Periodic Cost) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.5	$ 1.6
Interest cost	5.1	6.6
Expected return on plan assets	(14.1)	(14.7)
Amortization of prior service cost	0.0	(0.1)
Amortization of net loss (gain)	6.5	4.8
Net periodic cost	(1.7)	(1.8)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment	(0.7)
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1
Interest cost	0.2	0.2
Expected return on plan assets	0.0	0.0
Amortization of prior service cost	(0.3)	(0.3)
Amortization of net loss (gain)	0.0	0.0
Net periodic cost	$ 0.0	$ 0.0