CONDENSED CONSOLIDATED STATEMENTS OF INCOME (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
OPERATING REVENUES [Abstract]
Gas utility	$ 117.7	$ 108.5	$ 530.8	$ 590.1
Electric utility	173.5	164.4	463.3	466.0
Nonutility	339.8	300.6	755.3	774.6
Total operating revenues	631.0	573.5	1,749.4	1,830.7
OPERATING EXPENSES [Abstract]
Cost of gas sold	29.1	27.3	174.6	235.8
Cost of fuel & purchased power	50.9	47.9	140.3	144.9
Cost of nonutility revenues	110.5	106.8	248.7	264.5
Other operating	256.3	234.3	686.9	690.5
Depreciation & amortization	65.4	65.0	193.4	191.6
Taxes other than income taxes	13.3	12.3	44.8	44.6
Total operating expenses	525.5	493.6	1,488.7	1,571.9
OPERATING INCOME	105.5	79.9	260.7	258.8
OTHER INCOME [Abstract]
Equity in (losses) of unconsolidated affiliates	0.1	0.6	0.2	0.6
Other income - net	7.6	4.0	22.0	14.7
Total other income	7.5	3.4	21.8	14.1
INTEREST EXPENSE	20.9	21.2	64.3	63.1
INCOME BEFORE INCOME TAXES	92.1	62.1	218.2	209.8
INCOME TAXES	30.7	22.8	76.2	77.7
NET INCOME AND COMPREHENSIVE INCOME	$ 61.4	$ 39.3	$ 142.0	$ 132.1
AVERAGE COMMON SHARES OUTSTANDING	82.8	82.7	82.8	82.7
BASIC AND DILUTED EARNINGS PER SHARE OF COMMON STOCK
BASIC	$ 0.74	$ 0.48	$ 1.71	$ 1.60
DILUTED	0.74	0.48	1.71	1.60
DIVIDENDS DECLARED PER SHARE OF COMMON STOCK	$ 0.40	$ 0.38	$ 1.20	$ 1.14