Consolidated Statements of Comprehensive Income (unaudited) (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]
Unrealized losses arising during the period, net of tax benefit of $-, $-, $-, and $0.2	$ 0.0	$ 0.0	$ 0.0	$ 0.2
Reclassification adjustments for losses included in net income, net of tax benefit of $-, $0.1, $0.3, and $0.5	0.0	0.1	0.3	0.5
Amortization of net actuarial losses, net of tax benefit of $0.5, $0.5, $0.9, and $1.0	$ 0.5	$ 0.5	$ 0.9	$ 1.0