Revenue (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Customer deposits	$ 1,100,000,000		$ 1,000,000,000.0
Long-term supply commitment	10 years
Credit memoranda issued	$ 41,000,000	$ 0
Revenue	2,391,000,000	$ 2,812,000,000
Other assets	1,413,000,000		1,487,000,000
Other Noncurrent Liabilities [Member]
Customer deposits	907,000,000		927,000,000
Other Current Liabilities [Member]
Customer deposits	$ 192,000,000		104,000,000
Accounting Standards Update 2014-09 [Member]
Revenue			(105,000,000)
Other assets			$ 212,000,000