Pension and Other Postretirement Benefit Plans - Assumptions Used to Determine Benefit Obligation and Net Periodic Benefit Costs (Details)		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Costs, Future Period		6.50%
Assumptions Used to Determine Benefit Obligation [Abstract]
Rate of Compensation Increase		3.61%	4.07%
Assumptions Used to Determine Net Periodic Benefit Costs [Abstract]
Expected Long-Term Return on Plan Assets	[1]	6.75%	7.25%	7.50%
Rate of Compensation Increase		4.06%	4.04%	4.03%
Discount Rate		2.62%	3.38%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.52%	4.67%	4.05%
Postretirement Health and Life [Member]
Health Care Trend Rates [Abstract]
Trend Rate		5.81%	6.06%
Ultimate Trend Rate		4.50%	4.50%
Year Ultimate Trend Rate Effective		2038	2038
Assumptions Used to Determine Net Periodic Benefit Costs [Abstract]
Expected Long-Term Return on Plan Assets	[1]	6.08%	6.51%	6.72%
Discount Rate		2.70%	3.45%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.45%	4.47%	3.86%
Postretirement Health and Life [Member] | Minimum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Costs, Future Period		5.20%
Postretirement Health and Life [Member] | Maximum [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Costs, Future Period		6.50%

[1] The expected long-term rates of return used to determine net periodic benefit expense for 2021 have been reduced to 6.50 percent for pension expense and 5.20 percent to 6.50 percent for postretirement health and life expense.