Supplemental Equity and Comprehensive Income Information - Dividends (Details) - $ / shares |
1 Months Ended | 3 Months Ended | 12 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2014 |
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2016 |
Sep. 30, 2016 |
Jun. 30, 2016 |
Mar. 31, 2016 |
Dec. 31, 2015 |
Sep. 30, 2015 |
Jun. 30, 2015 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Supplemental Equity and Comprehensive Income Information | |||||||||||||||
| Dividends that have been declared but paid in subsequent period (in dollars per share) | $ 1.025 | ||||||||||||||
| Dividends declared in current period (in dollars per share) | $ 1.175 | $ 1.175 | $ 1.175 | $ 1.175 | $ 1.11 | $ 1.11 | $ 1.11 | $ 1.11 | $ 1.025 | $ 1.025 | $ 1.025 | $ 4.70 | $ 4.44 | $ 3.075 | |