Pension and Postretirement Health and Life Benefits (Schedule of Changes in Projected Benefit Obligations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Actuarial (gain) loss from remeasurement, net	$ 25.8	$ (1.4)
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan, Benefit Obligation	817.9	814.6	$ 832.8
Actuarial (gain) loss from remeasurement, net	32.8	19.1
Defined Benefit Plan, Service Cost	3.7	3.8
Defined Benefit Plan, Interest Cost	32.2	35.4
Defined Benefit Plan, Benefit Obligation, Benefits Paid	59.3	60.9
Defined Benefit Plan, Lump Sum Benefits Paid	(2.9)	(12.2)
Defined Benefit Plan, Administrative Expenses Paid	(3.2)	(3.4)
Defined Benefit Plan, Fair Value of Plan Assets	654.6	634.1	656.3
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	84.4	50.2
Defined Benefit Plan, Plan Assets, Contributions by Employer	1.5	4.1
Defined Benefit Plan, Plan Assets, Benefits Paid	59.3	60.9
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(163.3)	(180.5)
Amounts Recognized In Current Liabilities	(1.7)	(0.6)
Amounts Recognized In Noncurrent Liabilities	(161.6)	(179.9)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	$ (163.3)	$ (180.5)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.70%	4.10%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Benefit Obligation	$ 170.7	$ 192.8	203.5
Actuarial (gain) loss from remeasurement, net	(24.8)	(9.2)
Defined Benefit Plan, Service Cost	0.0	0.0
Defined Benefit Plan, Interest Cost	7.2	8.2
Defined Benefit Plan, Benefit Obligation, Benefits Paid	14.5	13.3
Defined Benefit Plan, Lump Sum Benefits Paid	0.0	0.0
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	10.0	3.6
Defined Benefit Plan, Administrative Expenses Paid	0.0
Defined Benefit Plan, Fair Value of Plan Assets	1.8	7.7	$ 13.8
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	0.1	0.5
Defined Benefit Plan, Plan Assets, Contributions by Employer	8.5	6.7
Defined Benefit Plan, Plan Assets, Benefits Paid	14.5	13.3
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(168.9)	(185.1)
Amounts Recognized In Current Liabilities	(14.7)	(13.8)
Amounts Recognized In Noncurrent Liabilities	(154.2)	(171.3)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	(168.9)	(185.1)
Recognized In Accumulated Other Comprehensive Income Pre Tax Prior Service Cost Credit	$ (2.5)	$ (2.6)
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.60%	3.90%