Pension and Other Benefits Pension assumptions (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assumptions used calculating net periodic benefit cost, discount rate	3.23%	3.57%	3.58%
Defined benefit plan, assumptions used calculating net periodic benefit cost, discount rate for interest cost	2.83%	3.09%	3.13%
Defined benefit plan, assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets	2.07%	2.91%	4.59%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted-Average Interest Crediting Rate	1.73%	2.75%	2.08%
Defined benefit plan, assumptions used calculating net periodic benefit cost, rate of compensation increase	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost initial pre-65 health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost initial post-65 health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost ultimate health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation, discount rate	2.51%	3.23%	4.25%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate	1.36%	1.73%	2.75%
Defined benefit plan, assumptions used calculating benefit obligation, rate of compensation increase	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation pre-65 initial health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation post-65 initial health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation ultimate health care cost trend rate	0.00%	0.00%	0.00%
Supplemental Employee Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assumptions used calculating net periodic benefit cost, discount rate	3.18%	4.32%	3.65%
Defined benefit plan, assumptions used calculating net periodic benefit cost, discount rate for interest cost	2.70%	3.88%	3.20%
Defined benefit plan, assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets	0.00%	0.00%	0.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted-Average Interest Crediting Rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost, rate of compensation increase	5.75%	5.75%	5.75%
Defined benefit plan, assumptions used calculating net periodic benefit cost initial pre-65 health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost initial post-65 health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost ultimate health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation, discount rate	2.41%	3.18%	4.32%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation, rate of compensation increase	5.75%	5.75%	5.75%
Defined benefit plan, assumptions used calculating benefit obligation pre-65 initial health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation post-65 initial health care cost trend rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation ultimate health care cost trend rate	0.00%	0.00%	0.00%
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assumptions used calculating net periodic benefit cost, discount rate	3.33%	4.41%	3.72%
Defined benefit plan, assumptions used calculating net periodic benefit cost, discount rate for interest cost	2.77%	3.91%	3.20%
Defined benefit plan, assumptions used calculating net periodic benefit cost, expected long-term rate of return on plan assets	0.00%	0.00%	0.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Weighted-Average Interest Crediting Rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost, rate of compensation increase	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating net periodic benefit cost initial pre-65 health care cost trend rate	6.79%	7.25%	7.75%
Defined benefit plan, assumptions used calculating net periodic benefit cost initial post-65 health care cost trend rate	7.51%	8.25%	7.75%
Defined benefit plan, assumptions used calculating net periodic benefit cost ultimate health care cost trend rate	4.50%	4.50%	4.50%
Defined benefit plan, assumptions used calculating net periodic benefit cost year that rate reaches ultimate pre-65 trend rate	2027	2025	2025
Defined benefit plan, assumptions used calculating net periodic benefit cost year that rate reaches ultimate post-65 trend rate			2027
Defined benefit plan, assumptions used calculating benefit obligation, discount rate	2.64%	3.33%	4.41%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation, rate of compensation increase	0.00%	0.00%	0.00%
Defined benefit plan, assumptions used calculating benefit obligation pre-65 initial health care cost trend rate	6.46%	6.79%	7.25%
Defined benefit plan, assumptions used calculating benefit obligation post-65 initial health care cost trend rate	7.08%	7.51%	8.25%
Defined benefit plan, assumptions used calculating benefit obligation ultimate health care cost trend rate	4.50%	4.50%	4.50%
Defined benefit plan, assumptions used calculating benefit obligation year that rate reaches ultimate pre-65 trend rate	2028	2027	2025