Acquisitions, Development and Divestitures - Discontinued Operations (Details) $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended		12 Months Ended	18 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2021 GBP (£)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)	Jun. 30, 2021 USD ($)	Jun. 14, 2021 USD ($)
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Income (Loss) from Discontinued Operations (net of income taxes)	$ (2)	$ 164			$ (1,490)	$ 705
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Total Assets	0				0		$ 18,983
Total Liabilities	0				0		11,023
Discontinued Operations, Held-for-sale | WPD
Discontinued Operation, Income (Loss) from Discontinued Operation Disclosures [Abstract]
Sales proceeds, net of realized foreign currency hedge losses			$ 10,732	£ 7,800,000,000
Proceeds from Daily Dividend, Divestiture of Business | £				548,000
Loss on Sale	0	0			(1,609)	0
Carrying value									$ 12,397
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Sale of Disposal Group, Net of Tax							4,000		3,600
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Operating Revenues	0	485			1,344	1,575
Operating Expenses	0	235			466	684
Other Income (Expense) - net	0	46			202	242
Interest Expense	0	88			209	271
Income before income taxes	0	208			871	862
Gain (Loss) on Sale	0	0			(1,609)	0
Income tax expense	2	44			752	157
Income (Loss) from Discontinued Operations (net of income taxes)	(2)	164			(1,490)	705
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Cash and cash equivalents							266
Accounts receivable and unbilled revenues							389
Price risk management assets							146
Property, plant and equipment, net							14,392
Goodwill							2,558
Other intangibles							413
Pension benefit asset							682
Other assets							137
Total Assets							18,983
Short-term debt and long-term debt due within one year							994
Accounts payable							220
Customer deposits							217
Accrued interest							190
Long-term debt							7,938
Total deferred income taxes							1,032
Price risk management liabilities							137
Other deferred credits and liabilities							295
Total Liabilities							11,023
Net assets							7,960
Gain (Loss) on Sale	$ 0	$ 0			$ (1,609)	$ 0
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Sale of Disposal Group, Net of Tax							4,000		$ 3,600
Net Proceeds From Divestiture Of Businesses			10,400
Proceeds from Divestiture of Businesses, before Foreign Currency Hedge Losses | £				£ 7,881,000,000
Disposal Group, Including Discontinued Operation, Loss on Foreign Currency Hedge Against Sale or Disposition								$ 386
Costs to sell			$ 69
Disposal Group, Including Discontinued Operation, Unrealized Gain (Loss) on Derivatives							$ 125