Summary of Significant Accounting Policies - Various Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Foreign Currency Transactions/Translation
Gain on revaluation of foreign currency transactions and monetary assets and liabilities	$ 16	$ 1	$ 1
Cash and Cash Equivalents and Restricted Cash
Outstanding checks included in accounts payable that were reclassified from cash and cash equivalents	$ 27	$ 38