Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Unrealized losses arising during the period, net of tax expense (benefit) of $0.1, $(0.2), $(0.1), and $(0.4)	$ 0.1	$ (0.2)	$ (0.1)	$ (0.4)
Reclassification adjustments for losses included in net income, net of tax benefit of $0.1, $0.2, $0.6, and $3.3	0.1	0.2	0.6	3.3
Amortization of net actuarial losses, net of tax benefit of $0.4, $0.5, $1.4, and $1.5	$ 0.4	$ 0.5	$ 1.4	$ 1.5