Revenues and Accounts Receivable - Counterparty Deficiencies (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Contract With Customer, Asset And Liability [Line Items]
Contract liability, deferred revenue	$ 501	$ 354	$ 338
Minimum Volume Commitments
Contract With Customer, Asset And Liability [Line Items]
Contract liability, deferred revenue	73	22
Counterparty deficiencies unbilled and uncollected	4	20
Counterparty deficiencies	$ 77	$ 42