Other Financial Statement Items - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Supplemental Balance Sheet Information [Line Items]
Loss from assets held for sale	$ 0	$ 10	$ 0	$ 15
Prepaid other taxes	84		84		$ 137
Deferred Payment Arrangements
Supplemental Balance Sheet Information [Line Items]
Accounts receivable	69		69		62
Allowance for doubtful accounts, deferred payment arrangement	$ 34		34		$ 32
Provision for doubtful accounts, accounts receivable		1	$ 2
Gas Trading and Storage Businesses
Supplemental Balance Sheet Information [Line Items]
Loss from assets held for sale		$ 10		$ 15