Summary of Significant Accounting Policies Asset Retirement Obligation (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Current Fiscal Year End Date		--12-31
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1		$ 63.3	$ 58.6
Accretion expense		2.8	2.6
Revisions in estimated cash flows	[1]	3.6	1.6
Additions		0.0	0.9
Liabilities settled		(0.1)	(0.4)
Balance at December 31		$ 69.6	$ 63.3

[1] Assumptions changed related to the estimated cost of asbestos abatement.