Description Of Business (Details)	9 Months Ended
	Sep. 30, 2017 mi agreement
Description Of Business [Line Items]
Electrification area | mi	400
International Brotherhood of Electrical Workers [Member]
Description Of Business [Line Items]
Number of collective bargaining agreements	3
Percentage of employees belonging to unions	70.00%
Expiration date of collective bargaining agreements	Jun. 30, 2021
Hotel Employees and Restaurant Employees [Member]
Description Of Business [Line Items]
Number of collective bargaining agreements	1
Expiration date of collective bargaining agreements	Jun. 30, 2021