Income Tax Matters, Narrative (Details) $ / shares in Units, $ in Millions					3 Months Ended			9 Months Ended
		May 26, 2016 $ / shares	Apr. 22, 2016	Apr. 07, 2016	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Income Tax Contingency
Income tax provision (benefit)					$ 9.4	$ 12.6		$ 40.2	$ (151.2)
Effective tax rate					38.70%	36.30%		37.50%	37.70%
Gross unrecognized tax benefits					$ 1.8			$ 1.8			$ 1.7
Gross unrecognized tax benefits that would impact effective tax rate					$ 0.7			$ 0.7			0.6
Cumulative-effect adjustment	[1]										$ 0.7
Accounting Standards Update 2016-09 | New Accounting Pronouncement, Early Adoption, Effect
Income Tax Contingency
Cumulative-effect adjustment	[1]									$ 0.7
Union VEBA
Income Tax Contingency
Income tax benefit on removal of Union VEBA net assets							$ 184.4		$ 184.4
Series A Junior Participating Preferred Stock
Income Tax Contingency
Preferred Stock, Rights Conversion Ratio into Preferred Stock				1
Preferred Stock, Redemption Price Per Share | $ / shares		$ 400.00
Preferred Stock, Rights Waiting Period, Duration Before Exercisable After Public Announcement		10 days
Preferred Stock, Rights Waiting Period, Duration Before Exercisable After Tender or Exchange Offer Results in Becoming an Acquiring Person		10 days
Value of right to purchase shares of the acquiring or other appropriate entity			2

[1] See Note 4 and Note 6 for discussion of our adoption of ASU 2016-09 (as defined in Note 1).