Summary of Significant Accounting Policies - Schedule of Cash and Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Cash and cash equivalents	$ 16,229	$ 19,384	$ 8,615	$ 6,268
Restricted cash included in prepaid expenses and other current assets	326	238	203	246
Restricted cash included in other non-current assets	270	279	288	269
Total as presented in the consolidated statements of cash flows	$ 16,825	$ 19,901	$ 9,106	$ 6,783