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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

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Percentage of public utility's approved equity to capital, including debt and equity.

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Percentage of public utility's approved return on equity.

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Percentage of public utility's requested return on equity.

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Regulatory Matters - Reliability Matters and FERC (Details) $ in Millions							1 Months Ended	3 Months Ended	9 Months Ended		12 Months Ended
	Oct. 13, 2017	Aug. 30, 2017 USD ($)	Mar. 10, 2017	Feb. 21, 2017	Jan. 19, 2017	Aug. 04, 2014	Jan. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($) entity condition subsidiary	Sep. 30, 2016 USD ($)	Dec. 31, 2012 USD ($)
Regulatory Matters [Line Items]
Regional enforcement entities \| entity									8
Impairment of assets (Note 14)									$ 162.0	$ 1,447.0
Purchase Agreement with Aspen Generating, LLC
Regulatory Matters [Line Items]
Cash purchase price		$ 825.0					$ 925.0
FES
Regulatory Matters [Line Items]
Impairment of assets (Note 14)									0.0	$ 540.0
MAIT
Regulatory Matters [Line Items]
Impairment of assets (Note 14)								$ 13.0
FERC
Regulatory Matters [Line Items]
Denied recovery charges of exit fees								78.8	$ 78.8
Number of conditions \| condition									1
Market-based rate authority renewal period									3 years
FERC \| PATH-Allegheny \| PATH Transmission Project
Regulatory Matters [Line Items]
Cost recovery, PP&E reclassified to Regulatory Assets											$ 62.0
FERC \| Path-WV \| PATH Transmission Project
Regulatory Matters [Line Items]
Cost recovery, PP&E reclassified to Regulatory Assets											$ 59.0
FERC \| PATH
Regulatory Matters [Line Items]
Approved ROE					8.11%
Requested return on equity				10.40%							10.40%
FERC \| PATH \| PATH Transmission Project
Regulatory Matters [Line Items]
Proposed return on equity											10.90%
Requested return on equity											10.40%
Return on equity granted for regional transmission organization participation											0.50%
Return on equity denied for regional transmission organization participation											0.50%
Remaining recovery period of regulatory assets											5 years
FERC \| FET
Regulatory Matters [Line Items]
Number of stand-alone transmission subsidiaries \| subsidiary									2
FERC \| The Ohio Companies \| ESP IV PPA
Regulatory Matters [Line Items]
Term of proposed purchase power agreement						8 years
FERC \| MAIT
Regulatory Matters [Line Items]
Approved suspension period			5 months
Approved ROE									11.00%
Impairment of assets (Note 14)								$ 13.0
FERC \| MAIT \| Subsequent Event
Regulatory Matters [Line Items]
Approved ROE	10.30%
Approved equity capital structure	60.00%
FERC \| JCP&L
Regulatory Matters [Line Items]
Approved suspension period			5 months