Capitalization - Narrative (Details)									1 Months Ended	3 Months Ended								12 Months Ended
	Nov. 08, 2019 $ / shares	Sep. 30, 2019 $ / shares shares	Aug. 01, 2019 shares	Jul. 22, 2019 shares	Jun. 03, 2019 USD ($)	May 21, 2019 USD ($)	Feb. 08, 2019 USD ($)	Jan. 31, 2018 USD ($)	Jan. 31, 2019 shares	Dec. 31, 2019 USD ($) $ / shares shares	Sep. 30, 2019 $ / shares	Jun. 30, 2019 $ / shares	Mar. 31, 2019 $ / shares	Dec. 31, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares	Jun. 30, 2018 $ / shares	Mar. 31, 2018 $ / shares	Dec. 31, 2019 USD ($) subsidiary $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Nov. 14, 2019 USD ($)	Aug. 15, 2019 USD ($)	Jun. 05, 2019 USD ($)	Apr. 15, 2019 USD ($)	Mar. 28, 2019 USD ($)	Jan. 10, 2019 USD ($)	Jan. 22, 2018 USD ($) $ / shares shares	Jun. 30, 2013 USD ($)
Debt Instrument [Line Items]
Retained earnings (accumulated deficit)										$ (3,967,000,000)				$ (4,879,000,000)				$ (3,967,000,000)	$ (4,879,000,000)
Dividends declared (in dollars per share) | $ / shares	$ 0.39																	$ 1.53	$ 1.82	$ 1.44
Common stock dividends per share paid, in dollars per share | $ / shares										$ 0.38	$ 0.38	$ 0.38	$ 0.38	$ 0.36	$ 0.36	$ 0.36	$ 0.36
FERC-defined equity to total capitalization ratio																		35.00%
Preferred shares, outstanding (in shares) | shares										0								0
Preference shares outstanding | shares										0				0				0	0
Repayments of debt																		$ 789,000,000	$ 2,608,000,000	$ 2,291,000,000
Number of subsidiaries that issued environmental control bonds | subsidiary																		2
Environmental control bonds outstanding										$ 333,000,000				$ 358,000,000				$ 333,000,000	358,000,000
Transition bond outstanding										$ 25,000,000				$ 41,000,000				25,000,000	$ 41,000,000
Principal default amount specified in debt covenants																		$ 100,000,000
Amount of private placement shares | shares										3,000,000				3,200,000				3,000,000	3,200,000	3,000,000.0							30,120,482
Common stock, par value (in dollars per share) | $ / shares										$ 0.1				$ 0.1				$ 0.1	$ 0.1								$ 0.10
Amount of private placement																											$ 850,000,000
Non-cash transaction: beneficial conversion feature (Note1)								$ 296,000,000										$ 0	$ 296,000,000	$ 0
Preferred stock, par value (in dollars per share) | $ / shares										$ 100				$ 100				$ 100	$ 100								$ 100
Liquidation preference value																											$ 1,000
Conversion price (in dollars per share) | $ / shares		$ 27.42									$ 27.42
Right to tender in 2021										$ 882,000,000								$ 882,000,000
Phase In Recovery Bonds
Debt Instrument [Line Items]
Long-term debt and other long-term obligations										268,000,000				$ 292,000,000				$ 268,000,000	$ 292,000,000
TrAIL and AGC
Debt Instrument [Line Items]
FERC-defined equity to total capitalization ratio																		45.00%
ME | Senior Notes | 4.30% Senior Notes Due 2029
Debt Instrument [Line Items]
Face amount of loan																										$ 500,000,000
Interest rate (percent)																										4.30%
ME | Senior Notes | 7.70% Senior Notes Due 2019
Debt Instrument [Line Items]
Face amount of loan																										$ 300,000,000
Interest rate (percent)																										7.70%
MP | PCRB
Debt Instrument [Line Items]
Right to tender in 2021										$ 73,500,000								$ 73,500,000
MP | FMBs | 155M FMB's, 3.23%, Due 2029
Debt Instrument [Line Items]
Face amount of loan																					$ 155,000,000
Interest rate (percent)																					3.23%
MP | FMBs | 45M FMB's, 3.93%, Due 2049
Debt Instrument [Line Items]
Face amount of loan																					$ 45,000,000
Interest rate (percent)																					3.93%
WP | FMBs | 155M FMB's, 4.22% Due 2059
Debt Instrument [Line Items]
Face amount of loan																						$ 150,000,000
Interest rate (percent)																						4.22%
WP | Senior Notes | 100M FMB's, 4.22% Due 2059
Debt Instrument [Line Items]
Interest rate (percent)						4.22%
Repayments of debt						$ 100,000,000
JCP&L | Senior Notes
Debt Instrument [Line Items]
Face amount of loan							$ 400,000,000
JCP&L | Senior Notes | 4.30% Senior Notes Due 2026
Debt Instrument [Line Items]
Interest rate (percent)							4.30%
JCP&L | Senior Notes | 7.35% Senior Notes Due 2019
Debt Instrument [Line Items]
Interest rate (percent)							7.35%
Repayments of debt							$ 300,000,000
FET | Senior Notes | 4.55% Senior Notes Due 2049
Debt Instrument [Line Items]
Face amount of loan																									$ 500,000,000
Interest rate (percent)																									4.55%
ATSI | Senior Notes | 4.38% Senior Notes Due 2031
Debt Instrument [Line Items]
Face amount of loan																								$ 100,000,000
Interest rate (percent)																								4.38%
Penn
Debt Instrument [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares										$ 100								$ 100
PN | Senior Notes | 3.60% Senior Notes Due 2029
Debt Instrument [Line Items]
Face amount of loan					$ 300,000,000
Interest rate (percent)					3.60%
PN | Senior Notes | 6.63% Senior Notes Due 2019
Debt Instrument [Line Items]
Interest rate (percent)					6.63%
Repayments of debt					$ 125,000,000
AGC | Senior Notes | 4.47% Senior Unsecured Notes Due 2029
Debt Instrument [Line Items]
Face amount of loan																							$ 50,000,000
Interest rate (percent)																							4.47%
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
Common Stock
Debt Instrument [Line Items]
Amount of private placement shares | shares														33,238,910					33,238,910
Amount of private placement																											3,000,000
Number of shares issued | shares		58,935,078	6,619,985	1,032,165					18,044,018
Other Paid-In Capital
Debt Instrument [Line Items]
Amount of private placement																											$ 847,000,000
Non-cash transaction: beneficial conversion feature (Note1)								$ 296,000,000							$ 296,000,000
Preferred Stock
Debt Instrument [Line Items]
Number of shares converted | shares		1,616,000		28,302					494,767										911,411
Series A Convertible Preferred Stock
Debt Instrument [Line Items]
Preferred stock shares issued | shares																											1,616,000
Preferred shares, outstanding (in shares) | shares			181,520							0				704,589				0	704,589
Preferred stock ownership cap (percent)		4.90%									4.90%
Amount of preferred stock investment																											$ 1,620,000,000
Series A Convertible Preferred Stock | Other Paid-In Capital
Debt Instrument [Line Items]
Amount of preferred stock investment																											1,460,000,000
Series A Convertible Preferred Stock | Preferred Stock
Debt Instrument [Line Items]
Amount of preferred stock investment																											$ 162,000,000