PROPERTY, PLANT, AND EQUIPMENT - Balances (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Property, plant, and equipment
Accumulated depreciation	$ 1,672.1	$ 1,620.5
Net property, plant, and equipment	4,544.5	4,150.1
Utility operations
Property, plant, and equipment
Accumulated depreciation	1,671.4	1,620.1
Net	4,294.7	3,983.6
CWIP	249.7	166.0
Net property, plant, and equipment	4,544.4	4,149.6
Utility operations \| Electric - generation
Property, plant, and equipment
Property, Plant And Equipment, Gross, Excluding Construction Work In Progress	2,840.0	2,831.2
Utility operations \| Electric - distribution
Property, plant, and equipment
Property, Plant And Equipment, Gross, Excluding Construction Work In Progress	1,738.3	1,510.0
Utility operations \| Natural gas - distribution, storage, and transmission
Property, plant, and equipment
Property, Plant And Equipment, Gross, Excluding Construction Work In Progress	995.2	910.6
Utility operations \| Other
Property, plant, and equipment
Property, Plant And Equipment, Gross, Excluding Construction Work In Progress	392.6	351.9
Non-utility operations
Property, plant, and equipment
Accumulated depreciation	0.7	0.4
Net property, plant, and equipment	0.1	0.5
Non-utility operations \| Other
Property, plant, and equipment
Property, Plant And Equipment, Gross, Excluding Construction Work In Progress	$ 0.8	$ 0.9

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Gross amount of long-lived physical assets used in the normal conduct of business and not intended for resale. Amount excludes construction work in progress. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Long-lived physical assets that are held by an entity, excluding construction work in progress, for use in the production or supply of goods and services, for rental to others, or for administrative purposes and that are expected to provide economic benefit for more than one year; net of accumulated depreciation.

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