Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Property, plant and equipment
Utility plant in service, at original costs	$ 10,018.7	$ 9,440.0
Construction work in progress	891.5	771.1
Accumulated depreciation	(2,826.1)	(2,676.8)
Utility plant in service, net	7,192.6	6,763.2
Other property	10.7	9.7
Total property, plant and equipment, net	7,203.3	6,772.9
Current assets
Cash and cash equivalents	9.5	9.1
Receivables, less allowance for uncollectibles of $1.2 and $1.5 at December 31, 2016 and 2015, respectively	205.6	227.9
Due from affiliates	6.9	63.6
Inventories, at average cost
Current derivative assets	15.1	0.0
Regulatory assets	28.1	44.3
Prepayments and other current assets	21.4	21.5
Total current assets	449.3	545.1
Deferred debits
Regulatory assets	392.6	373.8
Other	37.4	16.8
Total deferred debits	430.0	390.6
Total assets	8,082.6	7,708.6
Capitalization
Common stock	2,455.4	2,305.4
Accumulated other comprehensive loss	(2.8)	(3.6)
Retained earnings	311.2	313.7
Total capital	2,763.8	2,615.5
Long-term debt, less amount due within one year	2,162.9	2,161.7
Total capital	4,926.7	4,777.2
Current liabilities
Long-term debt due within one year	0.0	83.3
Notes payable	170.0	61.0
Accounts payable	262.1	205.7
Due to affiliates	25.2	16.9
Customer deposits	146.0	176.3
Regulatory liabilities	154.2	83.2
Derivative liabilities	0.0	24.1
Accrued interest	16.2	16.9
Accrued taxes	12.2	12.2
Other	10.3	10.2
Total current liabilities	796.2	689.8
Deferred credits
Deferred income taxes	1,406.6	1,308.8
Investment tax credits	11.4	10.5
Regulatory liabilities	590.6	603.5
Deferred credits and other liabilities	351.1	318.8
Total deferred credits	2,359.7	2,241.6
Commitments and Contingencies (see Note 9)
Total liabilities and capital	8,082.6	7,708.6
Fuel [Member]
Inventories, at average cost
Utility inventories	77.0	105.6
Materials and Supplies [Member]
Inventories, at average cost
Utility inventories	85.7	73.1
Electric [Member]
Property, plant and equipment
Utility plant in service, at original costs	7,623.7	7,270.3
Gas [Member]
Property, plant and equipment
Utility plant in service, at original costs	$ 1,503.5	$ 1,398.6