CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Current Assets [Abstract]
Cash & cash equivalents	$ 34.4	$ 74.7
Accounts receivable - less reserves of $5.4 & $5.6, respectively	227.9	227.5
Accrued unbilled revenues	94.5	142.5
Inventories	137.3	133.7
Recoverable fuel & natural gas costs	22.9	0.0
Prepayments & other current assets	63.2	81.0
Total current assets	580.2	659.4
Utility Plant [Abstract]
Original cost	6,419.8	6,090.4
Less: accumulated depreciation & amortization	2,527.3	2,415.5
Net utility plant	3,892.5	3,674.9
Investments in unconsolidated affiliates	20.4	20.9
Other utility & corporate investments	35.7	31.2
Other nonutility investments	16.1	16.2
Nonutility plant - net	420.8	414.6
Goodwill	293.5	293.5
Regulatory assets	290.0	249.4
Other assets	42.7	39.9
TOTAL ASSETS	5,591.9	5,400.0
Current Liabilities [Abstract]
Accounts payable	266.3	248.8
Refundable fuel & natural gas costs	0.0	7.9
Accrued liabilities	184.8	183.6
Short-term borrowings	131.2	14.5
Current maturities of long-term debt	0.0	73.0
Total current liabilities	582.3	527.8
Long-term Debt - Net of Current Maturities	1,713.8	1,712.9
Deferred Credits & Other Liabilities [Abstract]
Deferred income taxes	874.8	805.4
Regulatory liabilities	450.9	433.9
Deferred credits & other liabilities	239.0	236.2
Total deferred credits & other liabilities	1,564.7	1,475.5
Common Shareholders' Equity [Abstract]
Commitments & Contingencies (Notes 7-11)
Common stock (no par value) – issued & outstanding 82.9 & 82.8, respectively	727.5	722.8
Retained earnings	1,004.8	962.2
Accumulated other comprehensive (loss)	(1.2)	(1.2)
Total common shareholders' equity	1,731.1	1,683.8
TOTAL LIABILITIES & SHAREHOLDERS' EQUITY	$ 5,591.9	$ 5,400.0

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Balance Type:	credit
Period Type:	instant

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.