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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121557415&loc=d3e14326-108349

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 25
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 30
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL MATTERS (Details) T in Millions, $ in Millions	3 Months Ended	12 Months Ended	15 Months Ended
	Mar. 31, 2021 USD ($) States performance_obligations compliance_option MW	Dec. 31, 2020 USD ($) T	Mar. 31, 2019 MW
Manufactured gas plant remediation
Regulatory assets \| $	$ 2,844.6	$ 2,803.3
National ambient air quality standards \| Electric
Air quality
Number of changes to the 2015 ozone standards \| performance_obligations	0
Number of revisions necessary to the 2012 standard for particulate matter \| performance_obligations	0
Climate change \| Electric
Air quality
Number of rules that regulate GHG emissions from electric generating units \| compliance_option	0
Company goal percentage met by the end of 2020 for carbon dioxide emissions reduction below 2005 levels	50.00%
Company goal for percent carbon dioxide emission reduction below 2005 levels by 2025	60.00%
Company goal for percentage of carbon dioxide emission reduction below 2005 levels by 2030	80.00%
Capacity of coal-fired generation retired, in megawatts \| MW			1,500
Capacity of fossil-fueled generation to be retired by 2025, in megawatts \| MW	1,800
Carbon dioxide emissions \| T		14.3
Climate change \| Natural gas
Air quality
Initial 2030 percentage goal for a reduction of methane emissions from a 2011 baseline	30.00%
Carbon dioxide emissions \| T		3.9
Cross state air pollution rule update rule revision \| Electric
Air quality
Number of states in Group 2 for CSAPR update rule revision \| States	9
Number of states affected by the CSAPR update rule revision \| States	21
Amount of further NOx reductions needed within the nine effected states \| performance_obligations	0
Steam electric effluent limitation guidelines \| Electric
Water quality
Number of new ELG rule requirements that affect our electric utilities \| performance_obligations	2
Expected capital investment to achieve required discharge limits \| $	$ 100.0
Manufactured gas plant remediation \| Natural gas
Manufactured gas plant remediation
Reserves for future environmental remediation \| $	10.3	$ 10.3
Manufactured gas plant remediation \| Natural gas \| Environmental remediation costs
Manufactured gas plant remediation
Regulatory assets \| $	$ 18.0	$ 18.5