Variable Interest Entities (Consolidated Information of Variable Interest Entity) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 102	$ 32
Accounts receivable	713	853
Prepayments and other current assets	130	104
Plant, property, and equipment, net	21,934	21,017
Total Assets	30,513	29,666
Accounts payable	787	661
Asset retirement obligations	599	553
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	15	7
Accounts receivable	8	5
Prepayments and other current assets	1	1
Plant, property, and equipment, net	675	692
Total Assets	699	705
Accounts payable	13	3
Asset retirement obligations	20	19
Total liabilities	$ 33	$ 22