COMPARABLE NINE-MONTH FINANCIAL INFORMATION (UNAUDITED) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended							9 Months Ended		12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Supplemental Income Statement Elements [Abstract]
Utility								$ 417.2	$ 390.6	$ 533.3	$ 451.6
Total Operating Revenues	59.4	93.9	263.9	142.7	48.4	104.5	237.7	417.2	390.6	533.3	451.6
Natural gas								184.5	163.4	215.5	142.2
Other operation and maintenance expenses								107.5	107.7	143.1	141.3
Depreciation and amortization								34.4	32.7	43.9	42.3
Taxes, other than income taxes								28.6	27.8	37.1	32.5
Total Utility Operating Expenses								355.0	331.6	439.6	358.3
Operating income (loss)	(12.1)	1.9	72.4	34.7	(22.5)	2.2	79.3	62.2	59.0	93.7	93.3
Other Income								2.2	13.2	14.0	2.7
Interest on long-term debt								10.1	10.1	13.5	13.7
Other interest charges								1.4	1.6	2.1	2.6
Total Interest Charges								11.5	11.7	15.6	16.3
Income Before Income Taxes								52.9	60.5	92.1	79.7
Income Tax Expense								19.9	22.9	34.7	30.3
Net Income	$ (9.4)	$ (0.6)	$ 43.0	$ 19.8	$ (8.9)	$ (0.7)	$ 47.2	$ 33.0	$ 37.6	$ 57.4	$ 49.4