Stock-Based Compensation (Schedule of Stock-Based Compensation Expense) (Details) - USD ($) shares in Millions, $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2015 |
Sep. 30, 2014 |
Sep. 30, 2015 |
Sep. 30, 2014 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | 10 | 10 | ||
| Pretax stock-based compensation expense | $ 14 | $ 12 | $ 47 | $ 44 |
| Tax benefit associated with stock-based compensation expense | 6 | 5 | 18 | 17 |
| Stock-based compensation costs capitalized | 1 | 1 | 3 | 3 |
| Restricted Stock Units Awards [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Pretax stock-based compensation expense | 9 | 8 | 29 | 30 |
| Performance Awards [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Pretax stock-based compensation expense | $ 5 | $ 4 | $ 18 | $ 14 |