REGULATORY MATTERS (Tables)

6 Months Ended

Jun. 30, 2017

Regulatory Assets and Liabilities Disclosure [Abstract]

Schedule of Changes in Net Regulatory Asset Balance

	Three months ended June 30,						Six months ended June 30,
	2017			2016			2017			2016
	(in millions)
Net regulatory asset (liability) balance at beginning of period	$	(34.1	)	$	31.2		$	11.9		$	29.9
Current period (over) under recovery revenue adjustments		12.0			5.9			(27.0	)		13.6
Amortization of prior year regulatory asset		(1.6	)		(7.8	)		(8.6	)		(14.2	)
Net regulatory asset (liability) balance at end of period	$	(23.7	)	$	29.3		$	(23.7	)	$	29.3