Operating Revenues (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Customer contracts, average remaining duration	11 years
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Customer contracts, term	5 years
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Customer contracts, term	15 years