Pension Benefits - Weighted Average Asset Allocation for Pension Plans (Details) - Pension Plans, Defined Benefit	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	100.00%	100.00%
Cash and Short-term Investments
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	2.00%	1.00%
Corporate Bonds and Notes
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	40.00%	41.00%
Common and Preferred Stocks
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	35.00%	37.00%
Bond Exchange Traded Funds
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	14.00%	6.00%
Other Assets
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	9.00%	15.00%