RISK MANAGEMENT - Undiscounted Cash Outflows Relating to Financial Liabilities (Details) $ in Millions	Sep. 30, 2026 CAD ($)
Accounts payable and accrued liabilities
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	$ 7,180
Accounts payable and accrued liabilities \| Less than 1 Year
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	7,180
Accounts payable and accrued liabilities \| Years 2 and 3
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	0
Accounts payable and accrued liabilities \| Years 4 and 5
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	0
Accounts payable and accrued liabilities \| Thereafter
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	0
Lease Liabilities
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	4,545
Lease Liabilities \| Less than 1 Year
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	525
Lease Liabilities \| Years 2 and 3
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	868
Lease Liabilities \| Years 4 and 5
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	644
Lease Liabilities \| Thereafter
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	2,508
Long-Term Debt
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	13,057
Long-Term Debt \| Less than 1 Year
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	395
Long-Term Debt \| Years 2 and 3
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	2,233
Long-Term Debt \| Years 4 and 5
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	1,373
Long-Term Debt \| Thereafter
Disclosure of Maturity Analysis for Financial Liabilities [Line Items]
Financial instruments	$ 9,056