CAPITALIZATION - Narrative (Details)					2 Months Ended	3 Months Ended								12 Months Ended
	Jan. 27, 2022 USD ($)	Jan. 20, 2022 USD ($)	Dec. 21, 2021 $ / shares	Nov. 06, 2021 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Sep. 30, 2021 $ / shares	Jun. 30, 2021 $ / shares	Mar. 31, 2021 $ / shares	Dec. 31, 2020 USD ($) $ / shares shares	Sep. 30, 2020 $ / shares	Jun. 30, 2020 $ / shares	Mar. 31, 2020 $ / shares	Dec. 31, 2021 USD ($) subsidiary $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 shares	Jan. 31, 2018 USD ($) $ / shares shares	Jun. 30, 2013 USD ($)
Debt Instrument [Line Items]
Retained earnings (accumulated deficit)					$ (1,605,000,000)	$ (1,605,000,000)				$ (2,888,000,000)				$ (1,605,000,000)	$ (2,888,000,000)
Dividends declared (in dollars per share) | $ / shares			$ 0.39											$ 1.56	$ 1.56	$ 1.53
Common stock dividends per share paid, in dollars per share | $ / shares						$ 0.39	$ 0.39	$ 0.39	$ 0.39	$ 0.39	$ 0.39	$ 0.39	$ 0.39
FERC-defined equity to total capitalization ratio														35.00%
Common stock, par value (in dollars per share) | $ / shares					$ 0.10	$ 0.10				$ 0.10				$ 0.10	$ 0.10
Preferred shares, outstanding (in shares) | shares					0	0				0				0	0
Preference shares outstanding (in shares) | shares					0	0				0				0	0
Preferred stock, par value (in dollars per share) | $ / shares					$ 100	$ 100								$ 100
Repayments of debt														$ 532,000,000	$ 1,114,000,000	$ 789,000,000
Number of subsidiaries that issued environmental control bonds | subsidiary														2
Environmental control bonds outstanding					$ 274,000,000	$ 274,000,000				$ 300,000,000				$ 274,000,000	$ 300,000,000
Principal default amount specified in debt covenants														$ 100,000,000
Series A Convertible Preferred Stock
Debt Instrument [Line Items]
Preferred stock shares issued (in shares) | shares																		1,616,000
Preferred stock, par value (in dollars per share) | $ / shares																		$ 100
Amount of preferred stock investment																		$ 1,620,000,000
Common Stock Purchase Agreement
Debt Instrument [Line Items]
Number of shares issued in transaction | shares				25,588,535
Common stock, par value (in dollars per share) | $ / shares				$ 0.10
Sale of stock, price per share (in dollars per share) | $ / shares				$ 39.08
Investment amount				$ 1,000,000,000
Transaction costs					26,000,000
Registered Shareholders, Directors and Employees of Subsidiaries
Debt Instrument [Line Items]
Share-based benefit plans (in shares) | shares														1,000,000	2,000,000	3,000,000
Phase In Recovery Bonds
Debt Instrument [Line Items]
Long-term debt and other long-term obligations					222,000,000	222,000,000				$ 245,000,000				$ 222,000,000	$ 245,000,000
Senior Notes | 4.25% Series B Senior Notes Due 2023
Debt Instrument [Line Items]
Face amount of loan					850,000,000	850,000,000								850,000,000
Debt premium					$ 38,000,000	$ 38,000,000								$ 38,000,000
Interest rate (percent)					4.25%	4.25%								4.25%
Senior Notes | 4.25% Series B Senior Notes Due 2023 | Subsequent Event
Debt Instrument [Line Items]
Repayments of debt		$ 850,000,000
Common Stock
Debt Instrument [Line Items]
Share-based benefit plans (in shares) | shares														1,000,000
Number of shares issued | shares																25,696,168	33,238,910
Preferred Stock
Debt Instrument [Line Items]
Number of shares converted | shares																704,589	911,411
Preferred Stock | Series A Convertible Preferred Stock
Debt Instrument [Line Items]
Amount of preferred stock investment																		162,000,000
OPIC | Series A Convertible Preferred Stock
Debt Instrument [Line Items]
Amount of preferred stock investment																		$ 1,460,000,000
Ohio Funding Companies
Debt Instrument [Line Items]
Aggregate annual servicing fees receivable for phase-in recovery bonds														$ 445,000
Ohio Funding Companies | Phase In Recovery Bonds
Debt Instrument [Line Items]
Face amount of loan																			$ 445,000,000
AGC
Debt Instrument [Line Items]
FERC-defined equity to total capitalization ratio														45.00%
CEI | Senior Notes | 2.77% Series A Senior Notes Due 2034 | Subsequent Event
Debt Instrument [Line Items]
Face amount of loan	$ 150,000,000
Interest rate (percent)	2.77%
TE | Senior Notes | 2.65%, 150 Million Notes Maturing 2028 | Subsequent Event
Debt Instrument [Line Items]
Prepayments of debt	$ 25,000,000
Interest rate (percent)	2.65%