Postretirement Benefits Other Than Pensions - Changes in Fair Value of Plan Assets and Changes in Accumulated Benefit Obligations (Details) - Other Postretirement Benefit Plan, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	$ 0.0	$ 0.0
Employer Contributions	3.4	3.4
Plan Participants' Contributions	1.2	1.2
Benefits Paid	(4.6)	(4.6)
Fair Value of Plan Assets at End of Year	0.0	0.0	$ 0.0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligations at Beginning of Year	31.1	35.1
Service Cost	0.2	0.2	0.2
Interest Cost	1.0	1.1	1.2
Plan Participants' Contributions	1.2	1.2
Benefits Paid	(4.6)	(4.6)
Medicare Part D Subsidy Received	0.3	0.1
Actuarial Losses (Gains)	0.4	(2.0)
Projected Benefit Obligation at End of Year	29.6	31.1	$ 35.1
Funded Status—Plan Assets in Excess (Deficit) of Projected Benefit Obligation	(29.6)	(31.1)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Gains (Losses), before Tax	$ (16.8)	$ (18.6)