ACQUISITION OF ASSETS OF COLUMBIA GAS OF MASSACHUSETTS - Schedule of Pro Forma Information (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares
Business Acquisition [Line Items]
Operating Revenues	$ 154.8
CMA
Business Acquisition [Line Items]
Operating Revenues	9,273.0
Net Income Attributable to Common Shareholders	$ 1,265.0
Basic EPS (in dollars per share) | $ / shares	$ 3.73
Diluted EPS (in dollars per share) | $ / shares	$ 3.72