Retirement And Other Employee Benefits (Effect Of One Percent Change In Assumed Health Care Cost) (Details) - Retirement Health Benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
One percentage point increase in health care cost trend rate
Effect on total of service and interest cost components	$ 0.0	$ 0.0	$ 0.0
Effect on postretirement benefit obligation	0.7	0.6	0.6
One percentage point decrease in health care cost trend rate
Effect on total of service and interest cost components	0.0	0.0	0.0
Effect on postretirement benefit obligation	$ (1.0)	$ (0.9)	$ (0.9)