Shares used to calculate earnings per share (Details) - shares shares in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Earnings Per Share [Abstract] | ||||
| Basic (shares) | 50.1 | 49.4 | 49.8 | 49.3 |
| Effect of dilutive stock options and awards (shares) | 0.6 | 0.5 | 0.6 | 0.0 |
| Diluted (shares) | 50.7 | 49.9 | 50.4 | 49.3 |
| Antidilutive stock options and awards excluded from denominator (shares) | 0.0 | 0.3 | 0.2 | 1.5 |
| Share-based goods and nonemployee services transaction, quantity of securities issued (shares) | 0.5 | 0.5 | 0.5 | 0.5 |