GOODWILL - Schedule of Goodwill by Reportable Segment (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill	$ 3,519,401	$ 3,519,401
Electric Distribution [Member]
Goodwill [Line Items]
Goodwill	2,500,000	2,500,000
Electric Transmission [Member]
Goodwill [Line Items]
Goodwill	600,000	600,000
Natural Gas Distribution [Member]
Goodwill [Line Items]
Goodwill	$ 400,000	$ 400,000