Transactions with Major Customers and Affiliates (Tables)

12 Months Ended

Dec. 31, 2017

Transactions with Major Customers and Affiliates [Abstract]

Schedule of revenue by major customers

Operating revenues received from three of our major customers in 2017, 2016 and 2015 are as follows (in millions):

	2017		2016		2015
Duke Energy Corporation	$	198.4	$	178.9	$	94.6
National Grid	177.4		166.3		129.6
The Southern Company, Inc.	160.0		69.6		61.6