Pension Benefits - Weighted Average Asset Allocation for Pension Plans (Details) - Pension Plans, Defined Benefit	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	100.00%	100.00%
Corporate Bonds and Notes
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	37.00%	40.00%
Common and Preferred Stocks
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	24.00%	35.00%
Bond Exchange Traded Funds
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	27.00%	14.00%
Cash and Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	2.00%	2.00%
Other Assets
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	10.00%	9.00%