CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Defined benefit pension and other postretirement plan adjustments, tax	$ (0.3)	$ 0.3	$ (0.7)	$ 0.9
Net gain on investment securities, tax	0.0	0.0	(2.9)	0.0
Net gains on derivatives, tax	$ (0.2)	$ (0.1)	$ (0.5)	$ 0.4