Other Postretirement Benefit Plans (Fair Value of Plan Assets and Funded Status of Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 19.8	$ 21.9	$ 24.9
Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated postretirement benefit obligation, beginning of year	10.1	11.6
Interest cost	0.4	0.4	0.5
Net actuarial gain	(0.9)	(0.3)
Benefits paid	(1.2)	(1.6)
Accumulated postretirement benefit obligation, end of year	8.4	10.1	$ 11.6
Fair value of plan assets, end of year	0.0	0.0
Funded status of plans	$ (8.4)	$ (10.1)