v2.3.0.11

Regulatory Matters (Details) (USD $)	1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended								0 Months Ended				0 Months Ended	12 Months Ended			0 Months Ended			1 Months Ended	0 Months Ended			3 Months Ended			6 Months Ended
	Aug. 25, 2010	Jun. 27, 2008	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Nov. 16, 2010	Oct. 21, 2009	Jul. 18, 2011 Margin Reduction During Test Year [Member]	Jul. 18, 2011 Test Year Margin [Member]	Jul. 18, 2011 Revenue Margin [Member]	Nov. 05, 2010 Maximum [Member]	Nov. 05, 2010 Minimum [Member]	Feb. 08, 2011 Columbia of Ohio [Member]	Feb. 23, 2010 Columbia of Ohio [Member]	Dec. 02, 2009 Columbia of Ohio [Member]	Apr. 27, 2011 Columbia of Ohio [Member]	Jul. 02, 2011 Columbia of Pennsylvania [Member]	Jun. 30, 2010 Columbia of Pennsylvania [Member]	Mar. 31, 2011 Columbia of Pennsylvania [Member]	Jan. 14, 2011 Columbia of Pennsylvania [Member]	Feb. 23, 2011 Northern Indiana [Member]	Nov. 04, 2010 Northern Indiana [Member]	Aug. 25, 2010 Northern Indiana [Member]	Dec. 29, 2010 Northern Indiana [Member]	Nov. 19, 2010 Northern Indiana [Member]	Oct. 21, 2009 Northern Indiana [Member]	Aug. 25, 2008 Northern Indiana [Member]	Mar. 31, 2011 Northern Indiana [Member]	Sep. 30, 2010 Northern Indiana [Member]	Mar. 31, 2010 Northern Indiana [Member]	Jun. 30, 2011 Northern Indiana [Member]	Jul. 18, 2011 Northern Indiana [Member]	Feb. 04, 2011 Northern Indiana [Member]	Dec. 09, 2009 Northern Indiana [Member]	Nov. 04, 2009 Northern Indiana [Member]	Oct. 29, 2009 Northern Indiana [Member]	Dec. 31, 2016 Columbia of Virginia [Member]	Dec. 31, 2015 Columbia of Virginia [Member]	Dec. 31, 2014 Columbia of Virginia [Member]	Dec. 31, 2013 Columbia of Virginia [Member]	Dec. 31, 2012 Columbia of Virginia [Member]	Dec. 31, 2011 Columbia of Virginia [Member]	May 03, 2010 Columbia of Virginia [Member]	Mar. 08, 2011 Columbia of Kentucky [Member]	Oct. 28, 2010 Columbia Gulf Rate Case [Member]	Apr. 09, 2009 Southern Indiana [Member]
Investments																																							$ 20,000,000	$ 20,000,000	$ 20,000,000	$ 20,000,000	$ 20,000,000	$ 2,900,000
Increase in revenue associated with AMRP Rider rate																																														500,000
Annual revenue increase base rate case								4,900,000														37,800,000																							13,000,000		50,000,000
Increased revenue associated with IRP and DSM Riders																		24,000,000
Potential impact to operating revenue from tariff modification																				3,700,000
Gas domestic regulated revenue			500,400,000	454,300,000	1,872,400,000	1,795,400,000													17,000,000				(800,000)	(14,900,000)
Monthly increase in fixed charge for residential customers													11.00	6.36
Depreciation					25,700,000
Period of contract for Substitute Natural Gas plant (in years)																																																30
Standard service offer auction final retail price															1.88	1.93
Refund to customers																					35,700,000												55,100,000				8,200,000	5,800,000
Computation of refund to customers as per IURC order																												one
Rejected computation of refund to customers as per IURC order									four
Number of standard service offer auction periods (in years)																	2
Original cost rate base																									2,639,000,000				2,706,000,000
Overall rate of return																									7.29%				7.70%
Allowed operating income																									192,400,000
Margin produced by rate base approval		85,700,000																							899,000,000		75,700,000
Construction work in progress																															600,000
Inventory raw materials and supplies write off																															2,900,000
Energy related inventory coal write off																															800,000
Bill credit that should coincide with IURC approval of new customer rate																																	55,000,000
Revenue requirement											817,000,000	926,500,000																						1,401,000,000
Current customer credit termination, pending settlement approval										59,000,000
Certain industrial special contracts expiration, pending settlement approval										32,800,000
Other revenue																																		46,000,000
Net revenue requirement from base rates																																		1,355,000,000
Base rate impact to residential customers																																		4.50%
Rate of return																																		6.98%
Return on equity																																		10.20%
Investment in Sugar Creek																																	330,000,000
Annual depreciation on Mitchell plant			8,602,900,000		8,602,900,000		8,492,600,000																										4,500,000
Deferred amortization balance period approved by IURC (in years)	five
Bill credits recognized for electric customers																														25,100,000		29,000,000
IURC set up overall annual energy savings goal to be achieved																																				2.00%
Overall annual energy savings goal achievement period, in years																																				10
Interim saving goal established in years																																				one
Deferred MISO costs																														5,700,000		4,800,000
Total deferred MISO costs																														42,300,000
Amount of purchased power costs exceeding benchmark amount recognized as net reduction																														0		200,000
Recovery costs relating to qualified pollution control projects																										514,000,000
Revised capital expenditure cost estimate approved by IURC																																			281,000,000
Operating and maintenance expenses							$ 27,000,000

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Amount of purchased power costs exceeding the benchmark amount recognized as a net reduction of revenues.

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Base rate impact to residential customers

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Bill Credit.

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Certain Industrial Special Contracts Expiration, Pending Settlement Approval

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Computation of refund to customers as per IURC order.

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Construction work in progress written off during period.

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Current Customer Credit Termination, Pending Settlement Approval

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Deferred Non Fuel Cost.

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Energy Related Inventory Coal Write Off.

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Increase in annual revenue claim for base rate.

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Increase in IRP and DSM Associated Rate.

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Increase in annual revenue associated with AMRP Rider Rate.

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Interim saving goal established in years.

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Inventory Raw Materials And Supplies Write Off.

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Margin produced by Base Rate approval based on 2007 test year volumes.

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Monthly Fixed Charge For Residential Customers

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Number of standard service offer auctions periods.

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Original Cost Rate Base

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Other Revenue

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Overall Annual Energy Savings Goal Achievement Period.

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Overall Annual Energy Savings Goal Percentage.

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Overall rate of return.

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Period of contract

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Potential Impact To Operating Revenue From Tariff Modification

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Public Utilities Property Plant And Equipment Plant Investment

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Rate of return

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Rejected computation of refund to customers as per IURC Order.

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Return On Equity

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Revenue requirement

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Revenue requirement, net

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Revised Capital Expenditure Cost Estimate

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Standard service offer auction final retail price.

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Current regulatory liabilities generally represent obligations to make refunds to customers for various reasons including overpayment.

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Noncurrent regulatory liabilities generally represent obligations to make refunds to customers for various reasons including overpayment.

+ References

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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Paragraph 28
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Revenue derived from the regulated (by a federal, state, or local government or agency) generation, transmission and distribution of [natural] gas.

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Sum of the carrying amounts as of the balance sheet date of all investments.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Period end book value of accumulated depreciation on property, plant and equipment (PPE) that is owned by the regulated operations of the public utility.

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The amortization period for recovery of the individual regulatory noncurrent asset in a schedule of regulatory noncurrent assets.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 71
-Paragraph 9, 10
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Amount of the estimated recovery from third parties recorded in the period for an individual site that reduces environmental remediation expense.

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Discloses the amount of operating expense for the period for routine plant maintenance and repairs.

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