Consolidated Statement of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Comprehensive Income (Loss), Tax, Portion Attributable to Parent, Parenthetical Disclosures [Abstract]
Adjustment to pension and other benefit plans tax impact	$ (1.0)	$ 18.9	$ 10.7
Unrealized gain (loss) on investment tax impact	(0.2)	0.1	0.2
Unrealized gain or loss on cash flow hedge tax impact	$ 0.4	$ 0.5	$ (0.3)