Capital Stock - Shares Used To Calculate Earnings (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Basic (shares)	50.7	50.0	49.3
Effect of dilutive stock awards (shares)	1.1	0.6	0.0
Diluted (shares)	51.8	50.6	49.3
Antidilutive stock options and awards excluded from denominator (shares)	0.1	0.1	1.7
Deferred compensation common stock unit (shares)	0.3	0.5	0.5