Employees - Fair Value Asset Allocation (Details)	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	100.00%	100.00%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	66.40%	78.50%
Debt securities
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	26.80%	13.00%
Real estate securities
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocation	6.80%	8.50%