Summary of Significant Accounting Policies - Notes and Accounts Receivable and Allowance for Doubtful Accounts (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Allowance for doubtful accounts on short-term and long-term accounts receivable	$ 32,000,000	$ 28,000,000
Allowance for doubtful accounts on short-term and long-term notes receivable	$ 0	$ 0