PENSION AND OTHER POSTRETIREMENT BENEFITS - EXPECTED BENEFIT PAYMENTS AND EMPLOYER CONTRIBUTIONS (Details) $ in Millions	Dec. 31, 2019 CAD ($)
Canada \| Pension
Benefits Expected to be Paid by the Company
Expected future benefit payments for 2020	$ 180
Expected future benefit payments for 2021	186
Expected future benefit payments for 2022	192
Expected future benefit payments for 2023	198
Expected future benefit payments for 2024	204
Expected future benefit payments for 2025-2029	1,105
Contributions expected to be paid in next fiscal year	104
Canada \| OPEB
Benefits Expected to be Paid by the Company
Expected future benefit payments for 2020	12
Expected future benefit payments for 2021	12
Expected future benefit payments for 2022	12
Expected future benefit payments for 2023	13
Expected future benefit payments for 2024	13
Expected future benefit payments for 2025-2029	69
Contributions expected to be paid in next fiscal year	12
United States \| Pension
Benefits Expected to be Paid by the Company
Expected future benefit payments for 2020	87
Expected future benefit payments for 2021	90
Expected future benefit payments for 2022	91
Expected future benefit payments for 2023	89
Expected future benefit payments for 2024	91
Expected future benefit payments for 2025-2029	402
Contributions expected to be paid in next fiscal year	31
United States \| OPEB
Benefits Expected to be Paid by the Company
Expected future benefit payments for 2020	23
Expected future benefit payments for 2021	22
Expected future benefit payments for 2022	21
Expected future benefit payments for 2023	20
Expected future benefit payments for 2024	19
Expected future benefit payments for 2025-2029	82
Contributions expected to be paid in next fiscal year	$ 8

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Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

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