Pension and Other Postretirement Benefit Plans - Components of Net Periodic Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service Cost	$ 10.1	$ 8.3	$ 9.9
Interest Cost	29.9	29.8	26.0
Expected Return on Plan Assets	(40.7)	(38.2)	(35.2)
Amortization of Loss	17.9	14.2	21.5
Amortization of Prior Service Cost (Credit)	0.2	0.3	0.3
Net Expense (Credit)	17.4	14.4	22.5
Postretirement Health and Life [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service Cost	4.3	3.4	3.9
Interest Cost	7.2	7.3	6.8
Expected Return on Plan Assets	(10.9)	(10.3)	(9.7)
Amortization of Loss	0.4	0.5	1.6
Amortization of Prior Service Cost (Credit)	(3.0)	(2.5)	(2.5)
Effect of Plan Settlement	0.0	0.0	(1.6)	[1]
Net Expense (Credit)	$ (2.0)	$ (1.6)	$ (1.5)

[1] Result of the termination of a legacy benefit plan.