Pension and Postretirement Health and Life Benefits Pension and Postretirement Health and Life Benefits (Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax	$ (0.3)	$ (0.3)
Pension Plan, Defined Benefit [Member]
Total recognized in net periodic benefit costs (income) and other comprehensive income (loss), pre-tax	8.1	(4.5)
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax	3.6
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax	0.3
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax	3.9	0.3
Total recognized in net periodic benefit costs (income) and other comprehensive income (loss), pre-tax	$ 2.0	$ (21.6)

Pension and Postretirement Health and Life Benefits Pension and Postretirement Health and Life Benefits (Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income) (Details) - USD ($)
$ in Millions

12 Months Ended

Dec. 31, 2016

Dec. 31, 2015

Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax

$ (0.3)

Pension Plan, Defined Benefit [Member]

Total recognized in net periodic benefit costs (income) and other comprehensive income (loss), pre-tax

8.1

(4.5)

Other Postretirement Benefit Plan, Defined Benefit [Member]

Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax

3.6