Pension Benefits - Weighted Average Asset Allocation for Pension Plans (Details) - Pension Plans, Defined Benefit [Member]	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	100.00%	100.00%
Cash and Short-term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	1.00%	2.00%
Corporate Bonds and Notes [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	41.00%	31.00%
Common and Preferred Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	37.00%	50.00%
Exchange Traded Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	6.00%	1.00%
Other Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	15.00%	16.00%