Revenue From Contracts with Customers Performance Obligations and Contract Balances (Details) - Environmental credits - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Contract with customer, liability, current	$ 27		$ 27		$ 14
Contract with customer, liability, revenue recognized	$ 2	$ 2	$ 2	$ 3