Capital Stock - Shares Used To Calculate Earnings (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Basic (shares)	50.4	50.2	50.9
Effect of dilutive stock awards (shares)	0.4	0.9	0.0
Diluted (shares)	50.8	51.1	50.9
Antidilutive stock options and awards excluded from denominator (shares)	0.6	0.1	1.6
Deferred compensation common stock unit (shares)	0.3	0.3	0.3