Summary of Significant Accounting Policies - Additional information (Details) - USD ($) $ in Millions |
12 Months Ended | |||
|---|---|---|---|---|
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
Jan. 01, 2019 |
|
| Accounting Policies [Abstract] | ||||
| Advertising expenses | $ 1,100 | $ 1,100 | $ 846 | |
| Amortization period of differences between the expected and actual return on plan assets | 5 years | |||
| Allowance for doubtful accounts | $ 46 | 51 | ||
| New Accounting Pronouncements or Change in Accounting Principle | ||||
| Other assets | 2,288 | 1,208 | ||
| Accounts payable and accrued liabilities | 11,832 | 11,931 | ||
| Other long-term liabilities | $ 17,597 | $ 14,490 | ||
| Accounting Standards Update 2016-02 | ||||
| New Accounting Pronouncements or Change in Accounting Principle | ||||
| Other assets | $ 405 | |||
| Accounts payable and accrued liabilities | 115 | |||
| Other long-term liabilities | $ 290 | |||