Consolidated Statements of Comprehensive Income (unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Unrealized losses arising during the period, tax expense (benefit)	$ (0.2)	$ 0.0	$ (0.4)	$ (0.5)
Reclassification adjustments for losses included in net income, tax benefit	0.2	1.9	3.3	6.6
Amortization of net actuarial losses, tax benefit	$ 0.5	$ 0.3	$ 1.5	$ 0.5