Stock Repurchases, Dividends and Earnings per Share - Share Repurchase Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|
| Equity [Abstract] | ||||
| Number of shares repurchased (in shares) | 3.3 | 2.1 | 7.1 | 3.7 |
| Amount paid | $ 219.5 | $ 131.8 | $ 474.0 | $ 230.7 |
| Weighted average cost per share (in dollars per share) | $ 67.47 | $ 62.87 | $ 67.05 | $ 61.81 |