COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL MATTERS (Details) $ in Millions	1 Months Ended				3 Months Ended
	Oct. 31, 2023 States mo	Aug. 31, 2023	Apr. 30, 2023 MMBTU	Dec. 31, 2020 micrograms	Mar. 31, 2024 USD ($) MW performance_obligations	Feb. 07, 2024 micrograms	Dec. 31, 2023 USD ($)	May 31, 2023 performance_obligations MW
Manufactured gas plant remediation
Regulatory assets					$ 2,859.4		$ 2,860.7
Environmental remediation costs
Manufactured gas plant remediation
Regulatory assets					$ 11.8		12.2
Cross State Air Pollution Rule - Good Neighbor Plan | Electric | Maximum
Air quality
RICE unit megawatts | MW					25
Mercury and Air Toxics Standards | Electric
Air quality
Current level of particulate matter in pounds per million british thermal unit | MMBTU			0.03
EPA proposed lower limit for particulate matter in pre-publication version of proposed rule | MMBTU			0.01
Even lower level of particulate matter that the EPA is seeking opinions on | MMBTU			0.006
National Ambient Air Quality Standards | Electric
Air quality
Number of states that failed to submit timely SIP revisions to address nonattainment areas classified as "moderate" for the 2015 standard | States	11
Timing of offset sanctions taking effect if the state SIP revision isn't approved | mo	18
Current number of micrograms per cubic meter that particulate matter needs to be below | micrograms				12
Current number of micrograms per cubic under 24-hour standard that fine particulate matter needs to be below | micrograms				35
National Ambient Air Quality Standards | Electric | Maximum
Air quality
Period of time for EPA review of ozone plan		5 years
New primary annual PM2.5 level | micrograms						9
National Ambient Air Quality Standards | Electric | Minimum
Air quality
Period of time for EPA review of ozone plan		3 years
Climate Change | Electric
Air quality
Number of applicable GHG performance standards for coal plants | performance_obligations								0
Percent capacity factor that if combined cycle natural gas plants are above it causes the rule to be highly dependent on hydrogen or carbon capture								50.00%
Percent capacity factor for simple cycle natural gas fired combustion turbines								20.00%
Rules that are being proposed for natural gas-fired stationary combustion turbines | performance_obligations								1
Number of subcategories of stationary combustion turbine unit annual capacity factors that the proposed rule will be divided into | performance_obligations								3
Capacity of coal-fired generation retired, in megawatts | MW					1,500
Capacity of fossil-fueled generation to be retired by the end of 2031, in megawatts | MW					1,800
Company goal for percent carbon emission reduction below 2005 levels by the end of 2025					60.00%
Company goal for percentage of carbon emission reduction below 2005 levels by the end of 2030					80.00%
Climate Change | Electric | Maximum
Air quality
RICE unit megawatts | MW								25
Steam Electric Effluent Limitation Guidelines | Electric
Water quality
Number of new ELG rule requirements that affect our electric utilities | performance_obligations					2
Compliance costs through 2023 associated with the ELG rule that were required to achieve discharge limits							97.0
Steam Electric Effluent Limitation Guidelines | Electric | Elm Road Generating Station
Water quality
Biological treatment system costs placed in service at ERGS							89.0
Manufactured Gas Plant Remediation | Natural gas
Manufactured gas plant remediation
Reserves for future environmental remediation (1)					$ 10.3		10.3
Manufactured Gas Plant Remediation | Natural gas | Environmental remediation costs
Manufactured gas plant remediation
Regulatory assets					$ 11.7		$ 12.2