Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Customer deposits	$ 1,100		$ 1,100		$ 1,000
Long-term supply commitment			10 years
Credit memoranda issued			$ 73	$ 37
Revenue	2,561	$ 2,940	4,952	$ 5,752
Other assets	1,417		1,417		1,487
Other Noncurrent Liabilities [Member]
Customer deposits	876		876		927
Other Current Liabilities [Member]
Customer deposits	$ 192		$ 192		104
Accounting Standards Update 2014-09 [Member]
Revenue					(105)
Other assets					$ 212