Variable Interest Entities (Consolidated Information of Variable Interest Entity) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 153	$ 32
Accounts receivable	745	853
Prepayments and other current assets	139	104
Plant, property, and equipment, net	21,533	21,017
Total Assets	29,953	29,666
Accounts payable	659	661
Asset retirement obligations	607	553
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	12	7
Accounts receivable	7	5
Prepayments and other current assets	1	1
Plant, property, and equipment, net	680	692
Total Assets	700	705
Accounts payable	10	3
Asset retirement obligations	20	19
Total liabilities	$ 30	$ 22