Summary of Significant Accounting Policies - Cash, Cash Equivalents, and Restricted Cash Reconciliation (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 8,307	$ 2,882	$ 1,565
Restricted cash included in prepaid expenses and other	192	212	47
Noncurrent Assets:
Cash restricted for airport construction	1,556	636	1,136
Total cash, cash equivalents and restricted cash	$ 10,055	$ 3,730	$ 2,748	$ 1,853