Variable Interest Entities (Consolidated Information of Variable Interest Entity) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 168	$ 140
Accounts receivable	863	886
Prepayments and other current assets	112	86
Plant, property, and equipment, net	21,039	18,926
Total Assets	29,666	26,837	$ 24,529
Accounts payable	671	622
Asset retirement obligations	553	$ 477
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	7
Accounts receivable	5
Prepayments and other current assets	1
Plant, property, and equipment, net	692
Total Assets	705
Accounts payable	3
Asset retirement obligations	19
Total liabilities	$ 22