Pension and Post-retirement Plans - Defined Benefit plan, Allocation of Investment Funds (Details) - Pension obligations	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Pension plan percentage by asset category	100.00%	100.00%
Canadian equities
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Pension plan percentage by asset category	42.00%	47.00%
Fixed income
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Pension plan percentage by asset category	57.00%	29.00%
Real estate and infrastructure
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Pension plan percentage by asset category	0.00%	14.00%
Other
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Pension plan percentage by asset category	1.00%	9.00%
Cash
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Pension plan percentage by asset category	0.00%	1.00%