Revenue - Narrative (Details) $ in Millions |
3 Months Ended | 6 Months Ended |
|---|---|---|
|
Jun. 30, 2018
USD ($)
|
Jun. 30, 2018
USD ($)
|
|
| Revenue from Contract with Customer [Abstract] | ||
| Adjustments to sales incentives for previously recognized revenue | $ 482 | $ 628 |
| Deferred revenue recognized | 402 | 785 |
| Deferred revenue expected to be recognized in the remainder of 2018 | 845 | 845 |
| Deferred revenue expected to be recognized in 2019 | 885 | 885 |
| Deferred revenue expected to be recognized in 2020 | 450 | 450 |
| Deferred revenue expected to be recognized thereafter | $ 569 | $ 569 |