Stock Repurchases, Dividends and Earnings per Share - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions |
1 Months Ended | 3 Months Ended | 6 Months Ended | |||||
|---|---|---|---|---|---|---|---|---|
Apr. 30, 2018 |
Oct. 31, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
Dec. 31, 2017 |
Sep. 30, 2017 |
|
| Equity [Abstract] | ||||||||
| Stock repurchased and pending settlement (in shares) | 200,000 | 100,000 | 200,000 | 100,000 | ||||
| Stock repurchased and pending settlement, liability | $ 10.3 | $ 6.6 | $ 10.3 | $ 6.6 | ||||
| Additional shares authorized for repurchase, value | $ 2,000.0 | |||||||
| Remaining authorized repurchase amount | $ 1,400.0 | $ 1,400.0 | $ 98.4 | |||||
| Quarterly dividend declared (in dollars per share) | $ 0.345 | $ 0.345 | $ 0.32 | $ 0.69 | $ 0.64 | |||
| Cash dividends declared | $ 225.7 | |||||||
| Quarterly dividend payable | $ 112.3 | $ 112.3 | $ 114.4 | |||||
| Options to purchase common stock (in shares) | 0 | 0 | 0 | 0 | ||||