Retirement and Compensation Plans Weighted average assumptions (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.37%	4.24%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	3.27%	3.21%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	4.24%	3.72%	4.29%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	6.00%	6.50%	6.60%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase	3.21%	3.27%	3.31%
Fixed income funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	47.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	49.00%
U.S. equity funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	30.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	29.00%
Alternative investments
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	8.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	5.00%
Liability Driven Investing Strategy
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	15.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	17.00%