Earnings Per Common Share (Details) - shares shares in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Maximum | ||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||
| Antidilutive securities excluded from computation of earnings per share, amount | 1 | 1 |