Stockholders' Equity (Repurchases of Common Stock Under Share Repurchase Programs) (Details) - USD ($) shares in Millions, $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Equity, Class of Treasury Stock [Line Items] | |||
| Total Share Repurchases | $ 1,418 | $ 885 | $ 996 |
| Total Share Repurchases | 7.2 | 5.5 | 7.7 |
| Share Repurchase Program [Member] | |||
| Equity, Class of Treasury Stock [Line Items] | |||
| Total Share Repurchases | $ 1,325 | $ 800 | $ 900 |
| Total Share Repurchases | 6.7 | 4.9 | 6.9 |
| Satisfy tax withholding [Member] | |||
| Equity, Class of Treasury Stock [Line Items] | |||
| Total Share Repurchases | $ 93 | $ 85 | $ 96 |
| Total Share Repurchases | 0.5 | 0.6 | 0.8 |