Other Comprehensive Income (Loss) and Accumulated Other Comprehensive Loss - Components of Other Comprehensive Income and Components of Accumulated Other Comprehensive Loss (Parenthetical) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Other comprehensive income (loss), net of total tax (benefit) expense	$ (0.2)	$ 0.5	$ 0.1	$ 0.7