Retirement Plans Retirement Plans (Weighted Average Assumptions Used to Determine Net Annual Benefit Cost) (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	4.28%	3.69%	4.19%
Service cost	3.81%	3.51%	4.13%
Interest cost	3.92%	3.34%	3.56%
Expected long-term rate of return on assets	7.46%	7.45%	7.43%
Rate of increase in compensation levels	2.77%	2.79%	2.90%
Other Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation	4.24%	3.64%	4.11%
Service cost	4.23%	3.79%	4.34%
Interest cost	3.88%	3.27%	3.43%
Expected long-term rate of return on assets	6.84%	7.75%	7.76%