Common Share Repurchases (details) - USD ($) $ / shares in Units, $ in Millions |
3 Months Ended | 9 Months Ended | |
|---|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2017 |
Apr. 20, 2017 |
|
| Common Share Repurchases disclosure | |||
| Number of shares repurchased (in shares) | 2,600,000 | 8,300,000 | |
| Cost of shares repurchased | $ 328.0 | $ 1,028.0 | |
| Average cost per share repurchased (in dollars per share) | $ 128.11 | $ 124.12 | |
| Number of shares acquired to cover tax withholding costs and exercise costs (in shares) | 964 | 500,000 | |
| Cost of shares acquired to cover tax withholding costs and exercise costs | $ 0.1 | $ 61.0 | |
| Additional share repurchase authorization | $ 5,000.0 | ||
| Remaining capacity under share repurchase authorization | $ 4,910.0 | $ 4,910.0 |