SIGNIFICANT ACCOUNTING MATTERS - Supplementary Cash Flow Information (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024
Cash Paid (Received) for:
Interest, Net of Capitalized Amounts	$ 1,315.1	$ 1,247.3
Income Taxes, Net	60.1	87.9
Sale of Transferable Tax Credits	(102.2)	(163.7)
Noncash Investing and Financing Activities:
Acquisitions Under Finance Leases	30.0	24.5
Construction Expenditures Included in Current Liabilities as of September 30,	1,168.8	1,015.1
Acquisition of Nuclear Fuel Included in Current Liabilities as of September 30,	$ 1.4	$ 8.2

Amount of cash paid for interest, excluding capitalized interest, classified as operating activity. Includes, but is not limited to, payment to settle zero-coupon bond for accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 17
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 25
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-25

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-2

Name:	us-gaap_InterestPaidNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration