Summary of Significant Accounting Policies - Schedule of Cash and Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 14,531	$ 6,268	$ 5,338	$ 3,686
Restricted cash included in prepaid expenses and other current assets	174	246	233	193
Restricted cash included in other non-current assets	298	269	255	398
Total as presented in the consolidated statements of cash flows	$ 15,003	$ 6,783	$ 5,826	$ 4,277