Pension And Other Postretirement Benefit Plans (Components Of Net Periodic Cost) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.5	$ 1.2
Interest cost	7.5	7.2
Expected return on plan assets	(16.4)	(13.9)
Amortization of prior service cost	(0.1)	(0.1)
Amortization of net loss (gain)	3.6	3.5
Net periodic cost	(3.9)	(2.1)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.0
Interest cost	0.3	0.1
Expected return on plan assets	0.0	0.0
Amortization of prior service cost	0.0	0.0
Amortization of net loss (gain)	(0.3)	(0.1)
Net periodic cost	0.1	0.0
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0
Interest cost	0.1	0.0
Expected return on plan assets	0.0	0.0
Amortization of prior service cost	0.0	0.0
Amortization of net loss (gain)	0.0	0.0
Net periodic cost	$ 0.1	$ 0.0