Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Dividends per share	$ 1.14	$ 0.92	$ 0.76
Retained Earnings [Member]
Dividends per share	$ 1.14	$ 0.92	$ 0.76
Accumulated Other Comprehensive Income (Loss) [Member]
Benefit for tax, pension and postretirement liability changes	$ 25.6	$ (24.7)	$ 2.7
Provision for tax, derivatives	$ (2.3)	$ (1.0)	$ 4.8