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