Pension and Other Postretirement Benefit Plans - Recurring Fair Value Measures, Activity in Level 3 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Pension [Member] | Private Equity Funds [Member]
Activity in Level 3 [Roll Forward]
Beginning Balance	$ 43.3	$ 46.8
Actual Return on Plan Assets	2.6	1.2
Purchases, Sales, and Settlements – Net	(2.6)	(4.7)
Ending Balance	43.3	43.3
Pension [Member] | Real Estate [Member]
Activity in Level 3 [Roll Forward]
Beginning Balance	28.9	26.5
Actual Return on Plan Assets	2.9	2.8
Purchases, Sales, and Settlements – Net	(2.9)	(0.4)
Ending Balance	28.9	28.9
Postretirement Health and Life [Member] | Private Equity Funds [Member]
Activity in Level 3 [Roll Forward]
Beginning Balance	12.9	13.1
Actual Return on Plan Assets	1.2	1.4
Purchases, Sales, and Settlements – Net	(2.1)	(1.6)
Ending Balance	$ 12.0	$ 12.9