CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues	$ 1,021.5	$ 1,005.5	$ 957.2
Operating expenses
Purchased power, affiliates	410.9	421.6	413.6
Cost of natural gas sold and transported	69.1	62.3	54.4
Operating and maintenance expenses	201.9	201.2	192.0
Conservation program expenses	12.3	12.6	12.7
Depreciation and amortization	126.1	111.2	98.3
Taxes (other than income taxes)	28.7	27.8	27.8
Total operating expenses	862.1	852.9	814.4
Operating income	159.4	152.6	142.8
Interest charges and financing costs
Interest charges — includes other financing costs of $1.8, $1,9, and $1.9, respectively	39.3	35.0	34.4
Public Utilities, Allowance For Funds Used During Construction, Capitalized Cost Of Debt	(4.1)	(2.8)	(1.8)
Total interest charges and financing costs	35.2	32.2	32.6
Other Income and Expenses [Abstract]
Other income, net	(3.1)	(3.5)	(2.5)
Allowance for funds used during construction — equity	9.2	6.7	4.3
Income before income taxes	130.3	123.6	112.0
Income taxes	32.3	44.2	42.9
Net income	98.0	79.4	69.1
Electricity, US Regulated [Member]
Revenues	720.7	704.7	679.5
Affiliate Revenue	157.9	177.2	170.4
Operating expenses
Cost of goods and services sold	13.1	16.2	15.6
Natural Gas, US Regulated [Member]
Revenues	141.6	122.4	106.2
Product and Service, Other [Member]
Revenues	$ 1.3	$ 1.2	$ 1.1