Variable Interest Entities (Consolidated Information of Variable Interest Entity) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Variable Interest Entity [Line Items]
Cash and cash equivalents	$ 496	$ 168
Accounts receivable	839	863
Prepayments and other current assets	145	112
Plant, property, and equipment, net	21,207	21,039
Total Assets	29,723	29,666
Accounts payable	538	671
Asset retirement obligations	564	553
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Cash and cash equivalents	8	7
Accounts receivable	9	5
Prepayments and other current assets	1	1
Plant, property, and equipment, net	686	692
Total Assets	704	705
Accounts payable	6	3
Asset retirement obligations	19	19
Total liabilities	$ 25	$ 22