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RELATED PARTY TRANSACTIONS (Details) - CAD ($) $ in Millions		12 Months Ended
	Oct. 31, 2024	Dec. 31, 2025	Dec. 31, 2024
Related Party Transaction [Line Items]
Ownership, percentage		100.00%	100.00%
Power purchased		$ 4,486	$ 4,143
Revenues		9,041	8,484
Capital contribution received from OPG		3	2
Transmission
Related Party Transaction [Line Items]
Revenues		2,429	2,269
Distribution
Related Party Transaction [Line Items]
Revenues		6,557	6,175
Province
Related Party Transaction [Line Items]
Dividends paid		370	350
Ministry
Related Party Transaction [Line Items]
Related party transaction amount		27	0
MOI
Related Party Transaction [Line Items]
Related party transaction amount	$ 400	19	43
IESO
Related Party Transaction [Line Items]
Power purchased		3,011	2,686
Funding received related to Conservation and Demand Management programs		0	1
IESO \| Amounts Related To Electricity Rebates
Related Party Transaction [Line Items]
Related party transaction amount		1,110	1,170
IESO \| Transmission
Related Party Transaction [Line Items]
Revenues		2,388	2,252
IESO \| Electricity, US Regulated
Related Party Transaction [Line Items]
Revenues		256	255
IESO \| Distribution
Related Party Transaction [Line Items]
Revenues		50	48
OPG
Related Party Transaction [Line Items]
Related party transaction amount		2	1
Power purchased		23	18
Capital contribution received from OPG		20	3
OPG \| Transmission
Related Party Transaction [Line Items]
Revenues		2	2
OPG \| Distribution
Related Party Transaction [Line Items]
Revenues		8	5
OPG \| Electric Other
Related Party Transaction [Line Items]
Revenues		2	1
OEFC
Related Party Transaction [Line Items]
Power purchased		2	1
OEB
Related Party Transaction [Line Items]
OEB fees		$ 14	$ 12
Province
Related Party Transaction [Line Items]
Ownership, percentage		47.10%	47.10%
Wataynikaneyap Power LP \| IESO \| Distribution
Related Party Transaction [Line Items]
Revenues		$ 133	$ 119