Pension and Other Postretirement Benefits - Assumptions (Details 2)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plans, Defined Benefit [Member]
Assumptions used to determine benefit obligations at December 31:
Discount rate		3.29%	4.22%	3.54%
Rate of compensation increase		4.00%	4.00%	4.00%
Interest crediting rate		3.80%	3.80%	3.80%
Assumptions used to determine pension and OPEB expense (income) for the year ended December 31:
Discount rate		4.14%	3.69%	3.93%
Expected return on plan assets		6.75%	7.00%	7.25%
Rate of compensation increase		4.00%	4.00%	4.00%
Interest crediting rate		3.80%	3.80%	3.80%
Other Postretirement Benefit Plans, Defined Benefit [Member]
Assumptions used to determine benefit obligations at December 31:
Discount rate		3.33%	4.27%	3.59%
Subsequent year healthcare cost trend rate		6.17%	6.50%	6.65%
Ultimate healthcare cost trend rate		4.50%	4.50%	4.50%
Year ultimate healthcare cost trend rate begins		2025	2025	2025
Assumptions used to determine pension and OPEB expense (income) for the year ended December 31:
Discount rate		4.27%	3.59%	4.04%
Forecast [Member] | Pension Plans, Defined Benefit [Member]
Assumptions used to determine pension and OPEB expense (income) for the year ended December 31:
Expected return on plan assets	7.50%