Other Comprehensive Income 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
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
OCI before reclassifications net of tax	$ 0.3	$ 0.2