Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Pension and other employee benefits, tax expense	$ 1.3	$ 0.0	$ 0.9	$ 0.0
Unrealized holding (loss)/gain on available-for-sale securities, tax expense (benefit)	(0.5)	(1.4)	1.7	(1.4)
Hedging activities, tax benefit	$ 0.5	$ 1.6	$ 3.2	$ 1.6