Condensed Consolidated Statements of Comprehensive Income (Loss) - 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]
Net income (loss)	$ 12.6	$ (11.1)	$ 42.8	$ (0.1)
Other comprehensive income:
Amortization of actuarial losses and prior service credits, net of income taxes	10.0	9.2	29.1	27.3
Comprehensive income (loss)	$ 22.6	$ (1.9)	$ 71.9	$ 27.2