Summary of Significant Accounting Policies - Schedule of Cash and Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 19,384	$ 6,268	$ 3,686
Restricted cash included in prepaid expenses and other current assets	238	246	193
Restricted cash included in other non-current assets	279	269	398
Total as presented in the consolidated statements of cash flows	$ 19,901	$ 6,783	$ 4,277	$ 3,965