Capital Stock - Shares Used To Calculate Earnings (Details) - shares shares in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
|
| Equity [Abstract] | ||||
| Basic (shares) | 51.1 | 50.7 | 51.0 | 50.7 |
| Effect of dilutive stock options and awards (shares) | 0.9 | 1.2 | 0.0 | 0.9 |
| Diluted (shares) | 52.0 | 51.9 | 51.0 | 51.6 |
| Antidilutive stock options and awards excluded from denominator (shares) | 0.0 | 0.0 | 1.6 | 0.1 |
| Share-based goods and nonemployee services transaction, quantity of securities issued (shares) | 0.3 | 0.3 | 0.3 | 0.3 |