Stock-Based Compensation - General Employees Stock Purchase Plan (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Share-based Compensation Arrangement by Share-based Payment Award Activity | |||
| Weighted-average fair value | $ 41.59 | $ 23.51 | $ 22.47 |
| Allocated Share Based Compensation Expense | $ 302 | $ 324 | $ 298 |
| General Employees' Stock Purchase Plan (GESPP) | |||
| Share-based Compensation Arrangement by Share-based Payment Award Activity | |||
| Number of shares authorized | 60 | ||
| Option price, percentage of market value at date of grant | 85.00% | ||
| Weighted-average fair value | $ 31.91 | $ 30.07 | $ 24.72 |
| Option price, discount from market value at date of grant | 15.00% | ||
| Allocated Share Based Compensation Expense | $ 30 | $ 26 | $ 24 |