Debt and Credit Agreements - Schedule of Outstanding Long-Term Debt (Details) - CAD ($) | 12 Months Ended | | |
Dec. 31, 2023 | Dec. 31, 2022 | Oct. 31, 2023 | Jun. 30, 2022 |
Debt Instrument [Line Items] | | | | |
Long-term debt, face amount | $ 15,020,000,000 | | | |
Long-term debt, total | 15,020,000,000 | $ 13,378,000,000 | | |
Add: Net unamortized debt premiums | 12,000,000 | 8,000,000 | | |
Add: Realized mark-to-market gain | 6,000,000 | 0 | | |
Less: Unamortized deferred debt issuance costs | (52,000,000) | (47,000,000) | | |
Total long-term debt | 14,986,000,000 | 13,339,000,000 | | |
Interest Rate Swap [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Add: Realized mark-to-market gain | 6,000,000 | | | |
Fixed-to-floating interest-rate swap | 425,000,000 | | $ 400,000,000 | |
Hydro One Sault Ste. Marie LP [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, face amount | 0 | 133,000,000 | | |
Long-term debt, market value | 0 | 133,000,000 | | |
Long-term debt issued | 0 | 0 | | |
Long-term debt repaid | 131,000,000 | 3,000,000 | | |
Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, face amount | 15,020,000,000 | 13,245,000,000 | | |
Debt instrument maximum borrowing capacity | | | | $ 4,000,000,000 |
Debt instrument unused borrowing capacity | 875,000,000 | | | |
Long-term debt issued | 2,375,000,000 | 750,000,000 | | |
Long-term debt repaid | $ 600,000,000 | $ 600,000,000 | | |
0.71% Series 48 Notes Due 2023 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 0.71% | 0.71% | | |
Long-term debt, face amount | $ 0 | $ 600,000,000 | | |
2.54% Series 42 Notes Due 2024 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 2.54% | 2.54% | | |
Long-term debt, face amount | $ 700,000,000 | $ 700,000,000 | | |
1.76% Series 45 Notes Due 2025 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 1.76% | 1.76% | | |
Long-term debt, face amount | $ 400,000,000 | $ 400,000,000 | | |
2.97% Series 40 Notes Due 2025 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 2.97% | 2.97% | | |
Long-term debt, face amount | $ 350,000,000 | $ 350,000,000 | | |
5.54% Series 57 Notes Due 2025 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 5.54% | 5.54% | | |
Long-term debt, face amount | $ 400,000,000 | $ 0 | | |
2.77% Series 35 Notes Due 2026 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 2.77% | 2.77% | | |
Long-term debt, face amount | $ 500,000,000 | $ 500,000,000 | | |
Floating-Rate Series 56 Notes Due 2026 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, face amount | $ 425,000,000 | $ 0 | | |
4.91% Series 52 Notes Due 2028 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.91% | 4.91% | | |
Long-term debt, face amount | $ 750,000,000 | $ 750,000,000 | | |
3.02% Series 43 Notes Due 2029 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 3.02% | 3.02% | | |
Long-term debt, face amount | $ 550,000,000 | $ 550,000,000 | | |
3.93% Series 53 Notes Due 2029 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 3.93% | 3.93% | | |
Long-term debt, face amount | $ 300,000,000 | $ 0 | | |
2.16% Series 46 Notes Due 2030 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 2.16% | 2.16% | | |
Long-term debt, face amount | $ 400,000,000 | $ 400,000,000 | | |
7.35% Debentures Due 2030 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 7.35% | 7.35% | | |
Long-term debt, face amount | $ 400,000,000 | $ 400,000,000 | | |
1.69% Series 49 Notes Due 2031 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 1.69% | 1.69% | | |
Long-term debt, face amount | $ 400,000,000 | $ 400,000,000 | | |
2.23% Series 50 Notes Due 2031 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 2.23% | 2.23% | | |
Long-term debt, face amount | $ 450,000,000 | $ 450,000,000 | | |
6.93% Series 2 Notes Due 2032 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 6.93% | 6.93% | | |
Long-term debt, face amount | $ 500,000,000 | $ 500,000,000 | | |
4.16% Series 54 Notes Due 2033 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.16% | 4.16% | | |
Long-term debt, face amount | $ 450,000,000 | $ 0 | | |
6.35% Series 4 Notes Due 2034 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 6.35% | 6.35% | | |
Long-term debt, face amount | $ 385,000,000 | $ 385,000,000 | | |
5.36% Series 9 Notes Due 2036 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 5.36% | 5.36% | | |
Long-term debt, face amount | $ 600,000,000 | $ 600,000,000 | | |
4.89% Series 12 Notes Due 2037 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.89% | 4.89% | | |
Long-term debt, face amount | $ 400,000,000 | $ 400,000,000 | | |
6.03% Series 17 Notes Due 2039 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 6.03% | 6.03% | | |
Long-term debt, face amount | $ 300,000,000 | $ 300,000,000 | | |
5.49% Series 18 Notes Due 2040 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 5.49% | 5.49% | | |
Long-term debt, face amount | $ 500,000,000 | $ 500,000,000 | | |
4.39% Series 23 Notes Due 2041 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.39% | 4.39% | | |
Long-term debt, face amount | $ 300,000,000 | $ 300,000,000 | | |
6.59% Series 5 Notes Due 2043 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 6.59% | 6.59% | | |
Long-term debt, face amount | $ 315,000,000 | $ 315,000,000 | | |
4.59% Series 29 Notes Due 2043 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.59% | 4.59% | | |
Long-term debt, face amount | $ 435,000,000 | $ 435,000,000 | | |
4.17% Series 32 Notes Due 2044 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.17% | 4.17% | | |
Long-term debt, face amount | $ 350,000,000 | $ 350,000,000 | | |
5.00% Series 11 Notes Due 2046 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 5% | 5% | | |
Long-term debt, face amount | $ 325,000,000 | $ 325,000,000 | | |
3.91% Series 36 Notes Due 2046 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 3.91% | 3.91% | | |
Long-term debt, face amount | $ 350,000,000 | $ 350,000,000 | | |
3.72% Series 38 Notes Due 2047 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 3.72% | 3.72% | | |
Long-term debt, face amount | $ 450,000,000 | $ 450,000,000 | | |
3.63% Series 41 Notes Due 2049 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 3.63% | 3.63% | | |
Long-term debt, face amount | $ 750,000,000 | $ 750,000,000 | | |
2.71% Series 47 Notes Due 2050 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 2.71% | 2.71% | | |
Long-term debt, face amount | $ 500,000,000 | $ 500,000,000 | | |
3.64% Series 44 Notes Due 2050 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 3.64% | 3.64% | | |
Long-term debt, face amount | $ 250,000,000 | $ 250,000,000 | | |
3.10% Series 51 Notes Due 2051 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 3.10% | 3.10% | | |
Long-term debt, face amount | $ 450,000,000 | $ 450,000,000 | | |
4.00% Series 24 Notes Due 2051 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4% | 4% | | |
Long-term debt, face amount | $ 225,000,000 | $ 225,000,000 | | |
4.46% Series 55 Notes Due 2053 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.46% | 4.46% | | |
Long-term debt, face amount | $ 300,000,000 | $ 0 | | |
4.85% Series 58 Notes Due 2054 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.85% | 4.85% | | |
Long-term debt, face amount | $ 500,000,000 | $ 0 | | |
3.79% Series 26 Notes Due 2062 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 3.79% | 3.79% | | |
Long-term debt, face amount | $ 310,000,000 | $ 310,000,000 | | |
4.29% Series 30 Notes Due 2064 [Member] | Medium Term Note Program [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.29% | 4.29% | | |
Long-term debt, face amount | $ 50,000,000 | $ 50,000,000 | | |
6.6% Senior Secured Bonds Due 2023 [Member] | Hydro One Sault Ste. Marie LP [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 6.60% | 6.60% | | |
Long-term debt, face amount | $ 0 | $ 0 | | |
Long-term debt, market value | $ 0 | $ 97,000,000 | | |
4.6% Note Payable Due 2023 [Member] | Hydro One Sault Ste. Marie LP [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Long-term debt, interest rate | 4.60% | 4.60% | | |
Long-term debt, face amount | $ 0 | $ 0 | | |
Long-term debt, market value | $ 0 | $ 36,000,000 | | |
Series 57 Notes Due 2025 [Member] | Medium Term Note Program [Member] | Interest Rate Swap [Member] | | | | |
Debt Instrument [Line Items] | | | | |
Fixed-to-floating interest-rate swap | | | $ 400,000,000 | |