Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Gain on defined benefit plans, income tax expense (benefit)		$ 2.8
Unrealized gain during period on derivatives qualified as cash flow hedges, income tax (expense) benefit	$ 1.3	1.2
Reclassification to net income of losses (gains) on cash flow hedges, income tax expense	$ 13.6	$ (16.6)