Stock-Based Compensation (Schedule of PSU Activity) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
Excess tax benefits recognized for share-based awards | $ 3 | $ 3 | $ 7 | $ 19 |
PSU | ||||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
Share units earned (in shares) | 154,189 | 171,080 | ||
Shares issued net of withholding taxes (in shares) | 94,399 | 99,805 | ||
Excess tax benefits recognized for share-based awards | $ 3 | $ 1 |