REVENUE (Details) $ in Millions		12 Months Ended
		Dec. 31, 2020 USD ($) company MW	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		$ 10,701	$ 10,805	$ 10,944
ARP		43	181	254
Other non-customer revenue		46	49	63
Total revenues	[1]	$ 10,790	11,035	11,261
Utility customer payment period		30 days
Other Non-Customer Revenue
Disaggregation of Revenue [Line Items]
Late payment charges		$ 31	37	39
Distribution services
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		5,171	5,050	5,055
Total revenues		8,688	8,720	8,937
Retail generation
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		3,517	3,670	3,882
Wholesale sales
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		260	423	524
Transmission
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		1,613	1,510	1,335
Total revenues		1,613	1,510	1,335
Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		140	152	148
Total revenues		489	805	989
Derivative Revenue | Other Non-Customer Revenue
Disaggregation of Revenue [Line Items]
Total revenues		$ 14	8	18
Utilities and FET
Disaggregation of Revenue [Line Items]
Number of existing utility operating companies | company		10
Megawatts of net demonstrated capacity of competitive segment (in MW's) | MW		3,790
Utilities and FET | Yard's Creek Energy, LLC Hydro Generation Facility
Disaggregation of Revenue [Line Items]
Megawatts of net demonstrated capacity of competitive segment (in MW's) | MW		210
Utilities and FET | Retail generation
Disaggregation of Revenue [Line Items]
Total revenues		$ 8,836	8,860	9,095
Utilities and FET | Retail generation | Residential
Disaggregation of Revenue [Line Items]
Total revenues		5,539	5,412	5,598
Utilities and FET | Retail generation | Commercial
Disaggregation of Revenue [Line Items]
Total revenues		2,140	2,252	2,350
Utilities and FET | Retail generation | Industrial
Disaggregation of Revenue [Line Items]
Total revenues		1,076	1,106	1,056
Utilities and FET | Retail generation | Other
Disaggregation of Revenue [Line Items]
Total revenues		81	90	91
Regulated Transmission
Disaggregation of Revenue [Line Items]
Total revenues		1,613	1,510	1,335
Regulated Transmission | Other
Disaggregation of Revenue [Line Items]
Total revenues		134	130	125
Regulated Transmission | ATSI
Disaggregation of Revenue [Line Items]
Total revenues		804	754	664
Regulated Transmission | TrAIL
Disaggregation of Revenue [Line Items]
Total revenues		247	242	237
Regulated Transmission | MAIT
Disaggregation of Revenue [Line Items]
Total revenues		250	224	150
Regulated Transmission | JCP&L
Disaggregation of Revenue [Line Items]
Total revenues		178	160	159
Operating Segments | Utilities and FET
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		9,227	9,421	9,741
ARP		43	181	254
Other non-customer revenue		93	96	108
Total revenues		9,363	9,698	10,103
Reduction in revenue		2	16	131
Operating Segments | Utilities and FET | Distribution services
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		5,259	5,133	5,159
Operating Segments | Utilities and FET | Retail generation
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		3,577	3,727	3,936
Operating Segments | Utilities and FET | Wholesale sales
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		251	411	502
Operating Segments | Utilities and FET | Transmission
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		0	0	0
Operating Segments | Utilities and FET | Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		140	150	144
Operating Segments | Regulated Transmission
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		1,613	1,510	1,335
ARP		0	0	0
Other non-customer revenue		17	16	18
Total revenues		1,630	1,526	1,353
Reduction in revenue		7	19	16
Operating Segments | Regulated Transmission | Distribution services
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		0	0	0
Operating Segments | Regulated Transmission | Retail generation
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		0	0	0
Operating Segments | Regulated Transmission | Wholesale sales
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		0	0	0
Operating Segments | Regulated Transmission | Transmission
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		1,613	1,510	1,335
Operating Segments | Regulated Transmission | Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		0	0	0
Corporate/Other and Reconciling Adjustments
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		(139)	(126)	(132)
ARP		0	0	0
Other non-customer revenue		(64)	(63)	(63)
Total revenues		(203)	(189)	(195)
Corporate/Other and Reconciling Adjustments | Distribution services
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		(88)	(83)	(104)
Corporate/Other and Reconciling Adjustments | Retail generation
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		(60)	(57)	(54)
Corporate/Other and Reconciling Adjustments | Wholesale sales
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		9	12	22
Corporate/Other and Reconciling Adjustments | Transmission
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		0	0	0
Corporate/Other and Reconciling Adjustments | Other
Disaggregation of Revenue [Line Items]
Total revenues from contracts with customers		$ 0	$ 2	$ 4

[1] Includes excise and gross receipts tax collections of $362 million, $373 million and $386 million in 2020, 2019 and 2018, respectively.