CONSOLIDATED STATEMENTS OF INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating revenues
Total operating revenues	$ 4,086.2	$ 4,042.5	$ 4,047.8
Operating expenses
Cost of natural gas sold and transported	428.4	458.7	425.4
Cost of sales — steam and other	15.3	16.1	15.9
Operating and maintenance expenses	787.5	760.8	759.7
Demand side management program expenses	142.2	125.0	118.2
Depreciation and amortization	561.1	471.5	443.6
Taxes (other than income taxes)	201.9	195.7	196.3
Total operating expenses	3,293.6	3,154.5	3,155.5
Operating income	792.6	888.0	892.3
Other income, net	2.1	7.8	1.1
Allowance for funds used during construction — equity	56.4	29.8	18.6
Interest charges and financing costs
Interest charges — includes other financing costs of $6.5, $6.3 and $6.3, respectively	207.9	190.7	181.6
Allowance for funds used during construction - debt	(22.2)	(11.4)	(7.0)
Total interest charges and financing costs	185.7	179.3	174.6
Income before income taxes	665.4	746.3	737.4
Income taxes	113.7	252.2	273.9
Net income	551.7	494.1	463.5
Electricity, US Regulated [Member]
Operating revenues
Total operating revenues	3,031.2	3,003.8	3,049.4
Operating expenses
Electric fuel and purchased power	1,157.2	1,126.7	1,196.4
Natural Gas, US Regulated [Member]
Operating revenues
Total operating revenues	1,014.6	995.2	957.7
Product and Service, Other [Member]
Operating revenues
Total operating revenues	$ 40.4	$ 43.5	$ 40.7