Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Millions |
Jan. 31, 2019 |
Jan. 01, 2019 |
Dec. 31, 2018 |
Jan. 01, 2018 |
Dec. 31, 2017 |
|---|---|---|---|---|---|
| New Accounting Pronouncements or Change in Accounting Principle | |||||
| Retained earnings | $ 40,636 | $ 39,115 | |||
| ASU 2016-16 Intra-Entity Transfers of Assets Other Than Inventory | Maximum | |||||
| New Accounting Pronouncements or Change in Accounting Principle | |||||
| Retained earnings | $ (2) | ||||
| ASU 2018-02 Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income | Forecast | |||||
| New Accounting Pronouncements or Change in Accounting Principle | |||||
| Cumulative effect of new accounting principle in period of adoption | $ 900 | ||||
| ASU 2016-02 Leases | Forecast | |||||
| New Accounting Pronouncements or Change in Accounting Principle | |||||
| Lease assets | $ 800 | ||||
| Lease liabilities | $ 800 | ||||
| Difference between Revenue Guidance in Effect before and after Topic 606 | Maximum | |||||
| New Accounting Pronouncements or Change in Accounting Principle | |||||
| Retained earnings | $ 2 |