Purchase of Variable Interest Entity - Consolidated Information of Variable Interest Entity (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 519	$ 140
Restricted cash and cash equivalents	39	17
Accounts receivable and accrued revenue, less allowance of $30 in 2020 and $20 in 2019	648	886
Plant, property, and equipment, net	20,630	18,926
Total Assets	29,280	26,837
Accounts payable	662	622
Asset retirement obligations	510	$ 477
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	3
Restricted cash and cash equivalents	12
Accounts receivable and accrued revenue, less allowance of $30 in 2020 and $20 in 2019	1
Plant, property, and equipment, net	696
Total Assets	712
Accounts payable	7
Asset retirement obligations	21
Total liabilities	$ 28