FINANCIAL CHARGES AND OTHER (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Expense, Nonoperating [Abstract]
Interest expense	$ 78.0	$ 88.0	$ 95.0
Net realized loss (gain) related to the interest rate swaps	7.0	(1.0)	(2.0)
PNGTS' amortization of loss on derivative instrument	0.0	0.0	1.0
AFUDC - Equity	(10.0)	(2.0)	(1.0)
Other (b)	(2.0)	(2.0)	(1.0)
Financial charges and other	73.0	83.0	92.0
Amortization of debt issuance costs and discounts	2.0	2.0	2.0
AFUDC debt	$ 1.3	$ 1.0	$ 1.0