RELATED PARTIES - UMERC (Details) - UMERC transfer $ in Millions	Jan. 01, 2017 USD ($) mile customer
Related parties
Miles of electric distribution lines transferred | mile	600
Miles of gas distribution mains transferred | mile	100
Transfer of net assets to affiliate | $	$ 20.6
Electric utility
Related parties
Number of customers | customer	9,000
Natural gas utility segment
Related parties
Number of customers | customer	5,300