Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Fair Value of Financial Instruments [Line Items]
Noncurrent liabilities - held for sale (Note 10)	$ 709	$ 691
Investments - held for sale (Note 10)	882	882
Investments not required to be disclosed	$ 297	$ 299
NUG contracts
Fair Value of Financial Instruments [Line Items]
Period of future observable data to determine contract price	2 years