Defined Benefit and Postretirement Benefits (Components Of Net Periodic Cost) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.4	$ 1.5	$ 4.1	$ 4.5
Interest cost	9.1	7.5	24.5	22.5
Expected return on plan assets	(11.6)	(16.4)	(40.2)	(49.1)
Amortization of prior service cost	0.1	(0.1)	(0.3)	(0.4)
Amortization of net loss (gain)	4.8	3.6	11.5	10.7
Net periodic cost	3.8	(3.9)	(0.4)	(11.8)
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.2	0.1	0.2	0.2
Interest cost	0.8	0.2	0.8	0.8
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of prior service cost	(0.8)	0.0	(0.8)	0.0
Amortization of net loss (gain)	(0.2)	(0.3)	(0.2)	(0.9)
Net periodic cost	0.0	0.0	0.0	0.1
Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	0.0	0.1	0.1	0.1
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of prior service cost	0.0	0.0	0.0	0.0
Amortization of net loss (gain)	0.0	0.0	(0.1)	0.0
Net periodic cost	$ 0.0	$ 0.1	$ 0.0	$ 0.1