CONDENSED STATEMENTS OF INCOME (Unaudited) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
REVENUES	[1]	$ 87.9	$ 89.3	$ 624.0	$ 605.8
OPERATING EXPENSES
Cost of natural gas sold (excluding operating expenses shown separately)	[1]	39.7	44.4	364.4	362.0
Other operations and maintenance	[1]	47.5	35.3	131.4	119.4
Depreciation and amortization		15.3	13.8	45.0	40.9
Other taxes		5.2	4.7	15.8	14.4
Total Operating Expenses		107.7	98.2	556.6	536.7
OPERATING INCOME (LOSS)		(19.8)	(8.9)	67.4	69.1
Interest and other income		0.9	1.3	2.8	3.6
Interest expense		7.3	7.0	22.5	21.2
INCOME (LOSS) BEFORE INCOME TAXES		(26.2)	(14.6)	47.7	51.5
Income taxes benefit/(expense)		8.5	5.8	(19.4)	(19.3)
NET INCOME (LOSS)		$ (17.7)	$ (8.8)	$ 28.3	$ 32.2

[1] See Note 9 for amounts attributable to affiliates