Employee Benefits, Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Details)		3 Months Ended												12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (percent)	[1]	2.70%	2.60%	3.25%	3.80%	4.00%	3.95%	3.85%	3.75%	3.25%	3.20%	3.30%	3.45%
Expected return on plan assets (percent)														7.00%	7.25%	7.25%
Rate of compensation increase (percent)														3.86%	3.86%	3.86%
SRP
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (percent)														4.10%	3.40%	3.85%
Expected return on plan assets (percent)														7.00%	7.25%	7.25%
Rate of compensation increase (percent)														3.86%	3.86%	3.86%
PBOP
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (percent)														4.30%	3.70%	4.20%
Expected return on plan assets (percent)														3.61%	5.30%	5.30%

[1] Pension expense was remeasured quarterly in 2019, 2018 and 2017. The quarterly remeasurements for each quarter in 2019, 2018 and 2017 were as follows: Quarter 1: 3.80%, 3.75% and 3.45%; Quarter 2: 3.25%, 3.85% and 3.30%; Quarter 3: 2.60%, 3.95% and 3.20%; and Quarter 4: 2.70%, 4.00% and 3.25%.