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COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL MATTERS (Details) $ in Millions	1 Months Ended	9 Months Ended
	Oct. 31, 2014 compliance_option	Sep. 30, 2018 USD ($) generating_units degreecelsius MW	Dec. 31, 2017 USD ($)
Climate Change | Electric
Air quality
Company goal for percentage of carbon dioxide emissions reduction		40.00%
Long-term company goal for percentage of carbon dioxide emissions reduction by 2050		80.00%
Capacity of coal generation expected to be retired by 2020 | MW		1,800
Climate Change | Electric | Maximum
Air quality
Global temperature increases limit | degreecelsius		2
Clean Water Act Cooling Water Intake Structure Rule | Electric
Water quality
Number of compliance options available to meet standard | compliance_option	7
Renewal period for facility permits		5 years
Steam Electric Effluent Limitation Guidelines | Electric
Water quality
Number of generating units of OCPP and ERGS | generating_units		6
Expected cost to achieve required emissions reductions		$ 70.0
Manufactured Gas Plant Remediation | Natural gas
Manufactured gas plant remediation
Regulatory assets recorded for remediation of manufactured gas plant sites		680.0	$ 676.6
Reserves recorded for remediation of manufactured gas plant sites		$ 617.4	$ 617.2

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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The percentage by which the company plans to reduce carbon dioxide emissions below 2005 levels by 2050

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Global temperature increases limit

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The percentage by which the company plans to reduce carbon dioxide emissions below 2005 levels by 2030.

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Total units of OCPP and ERGS

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