CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 385.0	$ 363.6	$ 300.4
Adjustments to reconcile net income to net cash provided from operating activities
Depreciation and amortization	374.8	307.7	291.3
Impairment of assets	0.4	6.3	1.1
Deferred income taxes and investment tax credits, net	143.7	166.0	146.4
Allowance for equity funds used during construction	(6.2)	(20.4)	(11.4)
(Gain) loss on disposition and abandonment of assets	4.2	(2.7)	0
Gain on insurance proceeds	(7.5)	(3.0)	0
Stock-based compensation	(2.6)	7.8	7.4
Excess tax benefit on stock-based compensation	0	0	(0.7)
Price risk management assets	3.3	(1.7)	3.9
Price risk management liabilities	(4.6)	19.0	8.5
Regulatory assets	20.3	14.0	24.1
Regulatory liabilities	(14.8)	(1.9)	(12.4)
Other assets	(6.9)	(7.6)	6.3
Other liabilities	(14.3)	(37.4)	(37.0)
Change in certain current assets and liabilities
Accounts receivable, net	27.1	(48.0)	11.9
Accrued unbilled revenues	1.9	(2.5)	0.4
Income taxes receivable	1.1	(3.6)	153.0
Fuel, materials and supplies inventories	13.7	54.2	(45.2)
Gas imbalance assets	(7.2)	0.7	0.7
Fuel clause under recoveries	1.8	(0.8)	(0.7)
Other current assets	(4.7)	(7.2)	(5.9)
Accounts payable	25.1	34.5	59.2
Gas imbalance liabilities	(4.8)	3.1	(5.3)
Fuel clause over recoveries	101.5	(22.2)	(157.6)
Other current liabilities	15.8	16.0	44.1
Net Cash Provided from Operating Activities	1,046.1	833.9	782.5
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures (less allowance for equity funds used during construction)	(1,150.6)	(1,270.4)	(879.9)
Acquisition of gathering assets	(78.6)	(200.4)	0
Proceeds from sale of assets	1.5	18.0	2.3
Proceeds from insurance	7.6	7.4	0
Reimbursement of capital expenditures	27.5	49.6	31.5
Net Cash Used in Investing Activities	(1,192.6)	(1,395.8)	(846.1)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from long-term debt	250.0	246.3	246.2
Increase (decrease) in short-term debt	153.8	132.1	(30.0)
Contributions from noncontrolling interest partners	46.2	216.4	183.2
Issuance of common stock	14.3	14.8	16.9
Proceeds from lines of credit	0	150.0	115.0
Retirement of long-term debt	0	0	(289.2)
Excess tax benefit on stock-based compensation	0	0	0.7
Payment of long-term debt	(0.1)	0	0
Purchase of treasury stock	(3.4)	(6.2)	0
Distributions to noncontrolling interest partners	(12.6)	(17.4)	(4.0)
Repayment of line of credit	(150.0)	(25.0)	(90.0)
Dividends paid on common stock	(154.5)	(146.8)	(141.0)
Net Cash Provided from Financing Activities	143.7	564.2	7.8
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	(2.8)	2.3	(55.8)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	4.6	2.3	58.1
CASH AND CASH EQUIVALENTS AT END OF PERIOD	$ 1.8	$ 4.6	$ 2.3