Employee Benefits Allocation of Plan Assets (Details)	Dec. 31, 2020	Dec. 31, 2019
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	100.00%
Defined benefit plan, actual plan asset allocations	100.00%	100.00%
Alternative Investments
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	23.00%
Defined benefit plan, actual plan asset allocations	24.00%	25.00%
Equity securities
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	27.00%
Defined benefit plan, actual plan asset allocations	27.00%	25.00%
Fixed income securities
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	19.00%
Defined benefit plan, actual plan asset allocations	18.00%	19.00%
Liability driven investments
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	15.00%
Defined benefit plan, actual plan asset allocations	15.00%	14.00%
Real estate
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	9.00%
Defined benefit plan, actual plan asset allocations	9.00%	9.00%
Other plan assets
Allocation of Plan Assets
Defined benefit plan, plan assets, target allocation, percentage	7.00%
Defined benefit plan, actual plan asset allocations	7.00%	8.00%