CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement Of Stockholders Equity [Abstract]
Stock based compensation expense and stock option plan transactions, income tax benefits	$ 15.8	$ 18.8	$ 13.4