NiSource (NI) 10-Q 31 Oct 13 2013 Q3 Quarterly report Financial data

Document_And_Entity_Informatio

Document And Entity Information	9 Months Ended
	Sep. 30, 2013	Oct. 24, 2013
Document Information [Line Items]	'	'
Document Type	'10-Q	'
Amendment Flag	'false	'
Document Period End Date	30-Sep-13	'
Document Fiscal Year Focus	'2013	'
Document Fiscal Period Focus	'Q3	'
Entity Registrant Name	'NISOURCE INC/DE	'
Entity Central Index Key	'0001111711	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Entity Common Stock, Shares Outstanding	'	313,294,844

Statements_Of_Consolidated_Inc

Statements Of Consolidated Income (USD $)	3 Months Ended		9 Months Ended
In Millions, except Share data in Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Net Revenues	'	'	'	'
Gas Distribution	$255.10	$226.30	$1,540.60	$1,382.60
Gas Transportation and Storage	346.9	278.3	1,181.90	1,043.70
Electric	413.4	418	1,175.20	1,147.70
Other	61.4	33.6	162.8	63.3
Gross Revenues	1,076.80	956.2	4,060.50	3,637.30
Cost of Sales (excluding depreciation and amortization)	243	227.2	1,268.30	1,090.30
Total Net Revenues	833.8	729	2,792.20	2,547
Operating Expenses	'	'	'	'
Operation and maintenance	468.9	418.6	1,375.60	1,208.20
Depreciation and amortization	144.5	125.3	431.4	418
Gain on sale of assets, net	-9.8	-0.7	-10.2	-3.8
Other taxes	64.3	62.3	221.7	215.3
Total Operating Expenses	667.9	605.5	2,018.50	1,837.70
Equity Earnings in Unconsolidated Affiliates	10.5	8	25.6	24.2
Operating Income	176.4	131.5	799.3	733.5
Other Income (Deductions)	'	'	'	'
Interest expense, net	-103.7	-107.9	-304.3	-314.4
Other, net	4.7	2.2	22.1	5.3
Total Other Deductions	-99	-105.7	-282.2	-309.1
Income from Continuing Operations before Income Taxes	77.4	25.8	517.1	424.4
Income Taxes	27.9	9.2	179.2	147.7
Income from Continuing Operations	49.5	16.6	337.9	276.7
Income from Discontinued Operations - net of taxes	0.1	2.7	7.5	5.4
(Loss) Gain on Disposition of Discontinued Operations - net of taxes	-1.5	0	34.9	0
Net Income	$48.10	$19.30	$380.30	$282.10
Basic Earnings (Loss) Per Share ($)	'	'	'	'
Continuing Operations	$0.16	$0.05	$1.08	$0.97
Discontinued operations	$0	$0.01	$0.14	$0.02
Basic Earnings Per Share	$0.16	$0.06	$1.22	$0.99
Diluted Earnings (Loss) Per Share ($)	'	'	'	'
Continuing operations	$0.16	$0.05	$1.08	$0.93
Discontinued operations	$0	$0.01	$0.14	$0.02
Earnings Per Share, Diluted	$0.16	$0.06	$1.22	$0.95
Dividends Declared Per Common Share	$0.25	$0.24	$0.98	$0.94
Basic Average Common Shares Outstanding	312,842	290,328	312,053	285,891
Diluted Average Common Shares	313,813	300,012	312,959	296,678

Statements_of_Consolidated_Com

Statements of Consolidated Comprehensive Income (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Net Income	$48.10		$19.30		$380.30		$282.10
Net unrealized (loss) gain on available-for-sale securities	0.9	[1]	0.7	[1]	-2.4	[1]	-1.8	[1]
Net unrealized gain on cash flow hedges	0.6	[2]	0.8	[2]	2	[2]	2.7	[2]
Unrecognized pension benefit and OPEB costs	0.1	[3]	0.7	[3]	5.5	[3]	2	[3]
Total other comprehensive income	1.6		2.2		5.1		2.9
Total Comprehensive Income	$49.70		$21.50		$385.40		$285
[1]	Net unrealized gain (loss) on available-for-sale securities, net of $0.5 million and $0.3 million tax expense in the third quarter of 2013 and 2012, respectively, and $1.3 million and $1.5 million tax benefit for the nine months ended September 30, 2013 and 2012, respectively.
[2]	Net unrealized gains on derivatives qualifying as cash flow hedges, net of $0.4 million and $0.6 million tax expense in the third quarter of 2013 and 2012, respectively, and $1.3 million and $1.8 million tax expense for the nine months ended September 30, 2013 and 2012, respectively.
[3]	Unrecognized pension benefit and OPEB costs, net of zero and $0.2 million tax expense in the third quarter of 2013 and 2012, respectively, and $3.5 million and $1.0 million tax expense for the nine months ended September 30, 2013 and 2012, respectively.

Statements_of_Consolidated_Com1

Statements of Consolidated Comprehensive Income (Parenthetical) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	$0.50	$0.30	($1.30)	($1.50)
Other Comprehensive Income Increase Decrease In Unrealized Gain Loss On Derivatives Arising During Period Tax	0.4	0.6	1.3	1.8
Change In Unrecognized Pension Benefit And OPEB Costs Tax	$0	$0.20	$3.50	$1

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Property, Plant and Equipment	'	'
Utility Plant	$22,869.70	$21,642.30
Accumulated depreciation and amortization	-9,258.60	-8,986.40
Net utility plant	13,611.10	12,655.90
Other property, at cost, less accumulated depreciation	301.3	260
Net Property, Plant and Equipment	13,912.40	12,915.90
Investments and Other Assets	'	'
Unconsolidated affiliates	327.8	243.3
Other investments	201.6	194.4
Total Investments and Other Assets	529.4	437.7
Current Assets	'	'
Cash and cash equivalents	14.9	36.3
Restricted Cash	18.3	46.8
Accounts receivable (less reserve of $20.2 and $24.0, respectively)	591	907.3
Income tax receivable	6.4	130.9
Gas inventory	454.8	326.6
Underrecovered gas and fuel costs	16.4	45
Materials and supplies, at average cost	99.9	97.4
Electric production fuel, at average cost	39.8	71.7
Price risk management assets	21.1	0.5
Exchange gas receivable	84.3	51.3
Assets of discontinued operations and assets held for sale	0	133.9
Regulatory assets	152.5	162.8
Prepayments and other	246.1	357.2
Total Current Assets	1,745.50	2,367.70
Other Assets	'	'
Price risk management assets	0	40.7
Regulatory assets	1,863.20	2,024.40
Goodwill	3,666.20	3,677.30
Intangible assets	278.4	286.6
Deferred charges and other	89	94.4
Total Other Assets	5,896.80	6,123.40
Total Assets	22,084.10	21,844.70
Common Stockholders' Equity	'	'
Common stock - $0.01 par value, 400,000,000 shares authorized; 313,135,192 and 310,280,867 shares outstanding, respectively	3.2	3.1
Additional paid-in capital	4,672.90	4,597.60
Retained earnings	1,133.80	1,059.60
Accumulated other comprehensive loss	-60.4	-65.5
Treasury stock	-48.6	-40.5
Total Common Stockholders' Equity	5,700.90	5,554.30
Long-term debt, excluding amounts due within one year	7,089.10	6,819.10
Total Capitalization	12,790	12,373.40
Current Liabilities	'	'
Current portion of long-term debt	541.2	507.2
Short-term borrowings	820.8	776.9
Accounts payable	369.6	538.9
Dividends payable	78.3	0
Customer deposits and credits	249.2	269.6
Taxes accrued	181.3	235.5
Interest accrued	71.6	133.7
Overrecovered gas and fuel costs	31.7	22.1
Price risk management liabilities	8.8	8.2
Exchange gas payable	207.3	146.2
Deferred revenue	21.3	42.8
Regulatory liabilities	75.5	171.6
Accrued liability for postretirement and postemployment benefits	6.1	6.1
Liabilities of discontinued operations and liabilities held for sale	0	108.6
Legal and environmental reserves	34.2	42.2
Other accruals	308.7	309.7
Total Current Liabilities	3,005.60	3,319.30
Other Liabilities and Deferred Credits	'	'
Price risk management liabilities	1.5	2.6
Deferred income taxes	3,133.50	2,953.30
Deferred investment tax credits	21.9	24.8
Deferred credits	94.9	84.1
Noncurrent deferred revenue	23.1	0
Accrued liability for postretirement and postemployment benefits	1,003.10	1,107.30
Regulatory liabilities and other removal costs	1,615.90	1,593.30
Asset retirement obligations	175.5	160.4
Other noncurrent liabilities	219.1	226.2
Total Other Liabilities and Deferred Credits	6,288.50	6,152
Commitments and Contingencies	0	0
Total Capitalization and Liabilities	$22,084.10	$21,844.70

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Accounts receivable less reserve	$20.20	$24
Common stock, par value	$0.01	$0.01
Common stock, shares authorized	400,000,000	400,000,000
Common Stock, Shares, Outstanding	313,135,192	310,280,867

Statements_Of_Consolidated_Cas

Statements Of Consolidated Cash Flows (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Operating Activities	'	'
Net Income	$380.30	$282.10
Adjustments to Reconcile Net Income to Net Cash from Continuing Operations:	'	'
Depreciation and amortization	431.4	418
Net changes in price risk management assets and liabilities	1.9	1.2
Deferred income taxes and investment tax credits	199.1	132.8
Deferred revenue	1.6	-0.7
Stock compensation expense and 401(k) profit sharing contribution	39.7	33
Gain on sale of assets	-10.2	-3.8
Income from unconsolidated affiliates	-25.5	-22.9
Gain on disposition of discontinued operations - net of tax	-34.9	0
Income from discontinued operations - net of taxes	-7.5	-5.4
Amortization of debt related costs	7	7.3
AFUDC equity	-12.7	-4.7
Distributions of earnings received from equity investees	19	25.1
Changes in Assets and Liabilities:	'	'
Accounts receivable	318.4	333.9
Income tax receivable	124.6	-55.1
Inventories	-103.7	19.6
Accounts payable	-177.7	-151
Customer deposits and credits	-20.4	-50
Taxes accrued	-68	-41.3
Interest accrued	-62.1	-29
Over(Under)recovered gas and fuel costs	38.1	-9.1
Exchange gas receivable/payable	28.1	-10.2
Other accruals	-36.5	-90.9
Prepayments and other current assets	45.5	48.3
Regulatory assets/liabilities	71.5	96.3
Postretirement and postemployment benefits	-95.9	-11.6
Deferred credits	11.1	7.6
Deferred charges and other noncurrent assets	11.8	28.1
Other noncurrent liabilities	-6.3	4.1
Net Operating Activities from Continuing Operations	1,067.70	951.7
Net Operating Activities used for Discontinued Operations	10.9	-9.9
Net Cash Flows from Operating Activities	1,078.60	941.8
Investing Activities	'	'
Capital expenditures	-1,297.30	-1,022.20
Proceeds from Insurance Settlement, Investing Activities	6.4	3
Proceeds from disposition of assets	17.9	23.6
Restricted cash withdrawals	28.5	95.8
Contributions to equity investees	-77.1	-11.3
Other investing activities	-48.4	-38.1
Net Investing Activities used for Continuing Operations	-1,370	-949.2
Net Investing Activities from (used for) Discontinued Operations	118.7	-2.1
Net Cash Provided by (Used in) Investing Activities, Total	-1,251.30	-951.3
Financing Activities	'	'
Issuance of long-term debt	815.3	991.4
Repayments of long-term debt and capital lease obligations	505.2	11.6
Premiums and other debt related costs	-3.2	-3.4
Change in short-term debt, net	43.9	-1,133.70
Issuance of common stock	36.1	376.4
Acquisition of treasury stock	-8	-10
Dividends paid - common stock	-227.6	-198.8
Net Cash Flows from (used for) Financing Activities	151.3	10.3
Change in cash and cash equivalents (used for) from continuing operations	-151	12.8
Cash contributions from (to) discontinued operations	129.6	-12
Cash and cash equivalents at beginning of period	36.3	11.5
Cash and Cash Equivalents at End of Period	$14.90	$12.30

Basis_of_Accounting_Presentati

Basis of Accounting Presentation	9 Months Ended
	Sep. 30, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Basis of Accounting Presentation	'
	Basis of Accounting Presentation
	The accompanying Condensed Consolidated Financial Statements (unaudited) for NiSource (the “Company”) reflect all normal recurring adjustments that are necessary, in the opinion of management, to present fairly the results of operations in accordance with GAAP in the United States of America.
	The accompanying financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in NiSource’s Annual Report on Form 10-K for the fiscal year ended December 31, 2012. Income for interim periods may not be indicative of results for the calendar year due to weather variations and other factors.
	The Condensed Consolidated Financial Statements (unaudited) have been prepared pursuant to the rules and regulations of the SEC. Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations, although NiSource believes that the disclosures made are adequate to make the information not misleading.

Recent_Accounting_Pronouncemen

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2013
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
Recent Accounting Pronouncements	'
	Recent Accounting Pronouncements
	There have been no recently issued accounting pronouncements which are expected to have a material impact on the Company's Condensed Consolidated Financial Statements (unaudited) or Notes to the Condensed Consolidated Financial Statements (unaudited).

Earnings_Per_Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Earnings Per Share	'
	Earnings Per Share
	Basic EPS is computed by dividing income available to common stockholders by the weighted-average number of shares of common stock outstanding for the period. The weighted average shares outstanding for diluted EPS includes the incremental effects of the various long-term incentive compensation plans and forward agreements, which were settled in the third quarter of 2012. The numerator in calculating both basic and diluted EPS for each period is reported net income. The computation of diluted average common shares follows:
		Three Months Ended		Nine Months Ended
		September 30,		September 30,
	(in thousands)	2013	2012	2013	2012
	Denominator
	Basic average common shares outstanding	312,842	290,328	312,053	285,891
	Dilutive potential common shares:
	Stock options	112	197	102	159
	Shares contingently issuable under employee stock plans	369	434	327	393
	Shares restricted under stock plans	490	654	477	626
	Forward agreements	—	8,399	—	9,609
	Diluted Average Common Shares	313,813	300,012	312,959	296,678

Discontinued_Operations_And_As

Discontinued Operations And Assets And Liabilities Held For Sale	9 Months Ended
	Sep. 30, 2013
Discontinued Operations And Assets And Liabilities Held For Sale [Abstract]	'
Discontinued Operations And Assets And Liabilities Held For Sale	'
	Discontinued Operations and Assets and Liabilities Held for Sale
	On September 1, 2013, NiSource sold the commercial and industrial natural gas portfolio of its unregulated natural gas marketing business. The sale included the physical contracts and associated financial hedges that comprise the portfolio, as well as the gas inventory and customer deposits of the business. For the three and nine months ended September 30, 2013, an after tax loss of $1.5 million was included in Loss on Disposition of Discontinued Operations, net of taxes in the Condensed Statements of Consolidated Income (unaudited). The assets and liabilities sold are classified as held for sale as of December 31, 2012. Refer to Note 7, "Risk Management Activities" for additional information regarding the price risk assets and liabilities of the business.
	During 2012, NiSource began marketing to sell the service plan and leasing business lines of its Retail Services business. As of December 31, 2012, the assets and liabilities of the business lines met the criteria to be classified as held for sale in accordance with GAAP. Additionally, the results of operations and cash flows were classified as discontinued operations. The sale of the business lines closed in January 2013 resulting in gain from the disposition of discontinued operations of $36.4 million, net of taxes, which was recorded during the first quarter of 2013.
	There were no assets and liabilities of discontinued operations and held for sale on the Condensed Consolidated Balance Sheet (unaudited) at September 30, 2013.
	The assets and liabilities of discontinued operations and held for sale on the Consolidated Balance Sheet at December 31, 2012 by segment were:
	(in millions)
	Assets of discontinued operations and held for sale:	Property, plant and			Price risk management assets			Other Assets			Total
		equipment, net
	Gas Distribution Operations	$	21.5		$	—		$	4.5		$	26
	Electric Operations	—			—			0.7			0.7
	Corporate and Other	—			107			0.2			107.2
	Total	$	21.5		$	107		$	5.4		$	133.9
	Liabilities of discontinued operations and held for sale:				Price risk management liabilities			Other Liabilities			Total
	Gas Distribution Operations				$	—		$	3.3		$	3.3
	Electric Operations				—			0.6			0.6
	Corporate and Other				104.7			—			104.7
	Total				$	104.7		$	3.9		$	108.6
	Total assets and liabilities of discontinued operations and held for sale in the table above relate to the commercial and industrial portfolio of NiSource's unregulated natural gas marketing business and the service plan and leasing business lines of NiSource's Retail Services business.
	Results from discontinued operations are provided in the following table. These results are primarily from NiSource's Retail Services business, a settlement at NiSource's former exploration and production subsidiary, CER, NiSource's unregulated natural gas marketing business and Columbia Propane. For additional information regarding the settlement refer to Note 17-B, “Other Legal Proceedings,” in the Notes to Condensed Consolidated Financial Statements (unaudited).
		Three Months Ended								Nine Months Ended
		September 30,								September 30,
	(in millions)	2013				2012				2013			2012
	Revenues from Discontinued Operations	$	0.4			$	10.8			$	1.3		$	28.8
	Income from discontinued operations	0.1				4.5				12.2			8.6
	Income tax expense	—				1.8				4.7			3.2
	Income from Discontinued Operations - net of taxes	$	0.1			$	2.7			$	7.5		$	5.4
	(Loss) Gain on Disposition of Discontinued Operations - net of taxes	$	(1.5	)		$	—			$	34.9		$	—

Asset_Retirement_Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2013
Asset Retirement Obligation [Abstract]	'
Asset Retirement Obligations	'
	Asset Retirement Obligations
	Certain costs of removal that have been, and continue to be, included in depreciation rates and collected in the service rates of the rate-regulated subsidiaries are classified as “Regulatory liabilities and other removal costs” on the Condensed Consolidated Balance Sheets (unaudited).
	Changes in NiSource’s liability for asset retirement obligations for the nine months ended September 30, 2013 and 2012 are presented in the table below:
	(in millions)	2013			2012
	Balance as of January 1,	$	160.4		$	146.4
	Accretion expense	0.9			0.8
	Accretion recorded as a regulatory asset/liability	6.5			6.6
	Additions	9.7			—
	Settlements	(1.3		)	(0.7		)
	Change in estimated cash flows	(0.7		)	(1.1		)
	Balance as of September 30,	$	175.5		$	152

Regulatory_Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 2013
Regulatory Assets and Liabilities Disclosure [Abstract]	'
Regulatory Matters	'
	Regulatory Matters
	Gas Distribution Operations Regulatory Matters
	Significant Rate Developments. On April 30, 2013, Indiana Governor Pence signed Senate Enrolled Act 560 into law. Among other provisions, this legislation provides for cost recovery outside of a base rate proceeding for new or replacement electric and gas transmission, distribution, and storage projects that a public utility undertakes for the purposes of safety, reliability, system modernization, or economic development. The cost recovery mechanism is referred to as a Transmission, Distribution and Storage System Improvement Charge or "TDSIC." Provisions of the TDSIC require that, among other things, requests for recovery include a seven year plan of eligible investments.  Once the plan is approved by the IURC, 80 percent of eligible costs can be recovered using a periodic rate adjustment mechanism.  Recoverable costs include a return on, and of, the investment, including AFUDC, post in service carrying charges, operation and maintenance expenses, depreciation, and property taxes.  The remaining 20 percent of recoverable costs are to be deferred for future recovery in the public utility’s next general rate case.  The periodic rate adjustment mechanism is capped at an annual increase of no more than two percent of total retail revenues. On October 3, 2013, Northern Indiana filed its gas TDSIC with the IURC. The filing included the seven year plan of eligible investments for a total of $710.0 million. An order is expected by the second quarter of 2014.
	On June 18, 2013, Northern Indiana, the OUCC and other customer stakeholder groups filed a unanimous agreement with the IURC to extend Northern Indiana's 2010 natural gas customer rate settlement through 2020. The Settlement Agreement was approved by order issued on August 28, 2013 with the stipulation that, on or before November 2020, Northern Indiana must file a general rate case.
	On April 15, 2013, Columbia of Ohio filed an application that seeks authority to reduce its Percentage of Income Payment Plan Rider. This revised rate, which will result in an annual reduction of revenues by approximately $6.7 million, became effective May 31, 2013.
	On April 15, 2013, Columbia of Ohio filed an application to reduce its Uncollectible Expense Rider by $16.5 million. On May 29, 2013, the PUCO issued an Entry that approved the revised Uncollectible Expense Rider.
	On April 1, 2013, Columbia of Ohio filed an application that seeks authority to recover the $8.2 million base chip transition cost currently deferred. By Order dated August 28, 2013, the PUCO approved Columbia of Ohio's application.
	On December 24, 2012, Columbia of Ohio filed an application for authority to continue its capital expenditure program in 2013 and succeeding years, and for the authority to defer the related post in-service carrying charges, depreciation expense, and property taxes on the assets of the capital expenditure program placed into service in 2013. The corresponding expenditures are expected to total approximately $8.0 million in 2013. By Order dated October 9, 2013, the PUCO approved the application.
	On November 30, 2012, Columbia of Ohio filed a Notice of Intent to file an application to adjust rates associated with its IRP and DSM Riders. Columbia of Ohio filed its Application on February 28, 2013 and indicated that Columbia of Ohio is seeking to increase revenues by approximately $29 million. A stipulation resolving all issues was filed on April 9, 2013, and a hearing was held on April 11, 2013. On April 24, 2013, the PUCO approved the stipulation.
	On May 29, 2013, Columbia of Kentucky filed an application with the Kentucky PSC requesting an increase of approximately $16.6 million in base rate revenues, the use of a forecasted test period and a revenue normalization adjustment to recognize changes in customer usage not included in Columbia of Kentucky's current weather normalization adjustment. The parties are engaged in settlement negotiations, and a hearing is scheduled for November 13, 2013. If approved, new rates are expected to go into effect in January 2014.
	On September 28, 2012, Columbia of Pennsylvania filed a base rate case with the Pennsylvania PUC, seeking a revenue increase of approximately $77.3 million annually and providing three options for residential rate design in order to mitigate revenue volatility associated with usage based rates. Columbia of Pennsylvania is the first utility in Pennsylvania to seek Pennsylvania PUC approval to design rates to recover costs that are projected to be incurred after the implementation of those new rates, as authorized by the Pennsylvania General Assembly with the passage of Act 11 of 2012. Accordingly, Columbia of Pennsylvania's filing sought to implement rates in July 2013 under which Columbia of Pennsylvania would immediately begin to recover costs that are projected for the twelve-month period ending June 30, 2014. On March 15, 2013, the parties to the rate case filed a joint petition formally seeking Pennsylvania PUC approval of a settlement featuring a revenue increase of $55.3 million annually and the implementation of a Weather Normalization Adjustment, whereby residential charges are adjusted in the event of winter temperatures that deviate from historic norms by plus or minus five percent. The Pennsylvania PUC issued an order approving the settlement on May 23, 2013, and new rates went into effect July 1, 2013.
	On July 3, 2013, the VSCC issued an order approving an amendment to Columbia of Virginia's infrastructure tracking mechanism pursuant to the Steps to Advance Virginia's Energy (“SAVE”) Plan Act. Columbia of Virginia's five year SAVE Plan provides for recovery of costs associated with the accelerated replacement of certain facilities designed to improve system safety or reliability through a rate rider. The amendment increases authorized annual investments by $5 million from 2013 through 2016, to $25 million per year. In addition, the amendment expands the types of infrastructure eligible for the tracking mechanism and affords Columbia of Virginia additional flexibility with respect to annual and total plan limitations on expenditures.
	On April 16, 2013, Columbia of Massachusetts submitted a filing with the Massachusetts DPU requesting an annual revenue requirement increase of $30.1 million. An order is expected by February 28, 2014, with new rates going into effect on March 1, 2014. Pursuant to the procedural schedule for this case, on September 3, 2013, Columbia of Massachusetts filed its updated revenue requirement of $29.5 million and on October 16, 2013, filed an updated cost of service for $30 million. Evidentiary hearings began on October 2, 2013.
	On September 3, 2013, Columbia of Massachusetts and the Massachusetts Office of the Attorney General filed a Joint Motion for Approval of a Settlement Agreement with the Massachusetts DPU which resolves issues related to the disposition of revenues realized by Columbia of Massachusetts in 2005 from MASSPOWER's buy-out of a special contract with Columbia of Massachusetts, and which are currently pending before the Massachusetts DPU in D.P.U. 10-10. The Settlement Agreement proposed to return $8.9 million to the customers of Columbia of Massachusetts in the form of a Distribution Rate Credit on their bills during the period November 1, 2013 through April 30, 2014. On October 16, 2013, the DPU issued an order approving the Settlement Agreement.
	On March 7, 2013, the Massachusetts DPU issued its final order approving $10.5 million of decoupling revenues for Columbia of Massachusetts' Peak Period RDAF that was effective November 1, 2012 through April 30, 2013.
	On February 27, 2013, Columbia of Maryland filed a base rate case with the Maryland PSC, seeking a revenue increase of approximately $5.3 million annually and seeking to implement a residential Revenue Normalization Adjustment in order to decouple revenues from customer usage and seeking to recover costs for environmental remediation associated with a former manufactured gas plant operated by a Columbia of Maryland predecessor in Hagerstown, Maryland, where a Columbia of Maryland service center is currently located. Hearings were held in June 2013. On September 23, 2013, the Maryland PSC issued an order that approved an annual revenue increase of $3.6 million, as well as Columbia of Maryland's proposed revenue normalization adjustment. The Maryland PSC permitted recovery of environmental remediation costs for the service center property, but denied recovery of the costs to acquire and remediate the adjacent property. On October 23, 2013, Columbia of Maryland filed a Petition for Judicial Review of the denial of the costs to acquire and remediate the adjacent property. New rates went into effect on September 25, 2013.
	Cost Recovery and Trackers. A significant portion of the distribution companies' revenue is related to the recovery of gas costs, the review and recovery of which occurs via standard regulatory proceedings. All states require periodic review of actual gas procurement activity to determine prudence and to permit the recovery of prudently incurred costs related to the supply of gas for customers. NiSource distribution companies have historically been found prudent in the procurement of gas supplies to serve customers.
	Certain operating costs of the NiSource distribution companies are significant, recurring in nature, and generally outside the control of the distribution companies. Some states allow the recovery of such costs via cost tracking mechanisms. Such tracking mechanisms allow for abbreviated regulatory proceedings in order for the distribution companies to implement charges and recover appropriate costs. Tracking mechanisms allow for more timely recovery of such costs as compared with more traditional cost recovery mechanisms. Examples of such mechanisms include GCR adjustment mechanisms, tax riders, gas energy efficiency programs, and bad debt recovery mechanisms.
	Comparability of Gas Distribution Operations line item operating results is impacted by regulatory trackers that allow for the recovery in rates of certain costs such as bad debt expenses. Increases in the expenses that are subject to trackers result in a corresponding increase in net revenues and therefore have essentially no impact on total operating income results.
	Certain of the NiSource distribution companies have completed rate proceedings involving infrastructure replacement or are embarking upon regulatory initiatives to replace significant portions of their operating systems that are nearing the end of their useful lives. Each LDC's approach to cost recovery may be unique, given the different laws, regulations and precedent that exist in each jurisdiction.
	Columbia Pipeline Group (formerly known as Gas Transmission and Storage) Operations Regulatory Matters
	Columbia Transmission Customer Settlement. On January 24, 2013, the FERC approved the Columbia Transmission Customer Settlement (the "Settlement"). In March 2013, Columbia Transmission paid $88.1 million in refunds to customers pursuant to the Settlement with its customers in conjunction with its comprehensive interstate natural gas pipeline modernization program. The refunds were made as part of the Settlement, which included a $50.0 million refund to max rate contract customers and a base rate reduction retroactive to January 1, 2012. Columbia Transmission expects to invest approximately $1.5 billion over a five-year period to modernize its system to improve system integrity and enhance service reliability and flexibility. The Settlement with firm customers includes an initial five-year term with provisions for potential extensions thereafter.
	The Settlement also provided for a depreciation rate reduction to 1.5% and elimination of negative salvage rate effective January 1, 2012 and for a second base rate reduction, which begins January 1, 2014, which equates to approximately $25 million in revenues annually thereafter.
	The Settlement includes a Capital Cost Recovery Mechanism (CCRM), a tracker mechanism that will allow Columbia Transmission to recover, through an additive capital demand rate, its revenue requirement for capital investments made under Columbia Transmission's long-term plan to modernize its interstate transmission system. The CCRM provides for a 14% revenue requirement with a portion designated as a recovery of increased taxes other than income taxes. The additive demand rate is earned on costs associated with projects placed into service by October 31 each year. The initial additive demand rate will be effective on February 1, 2014. The CCRM will give Columbia Transmission the opportunity to recover its revenue requirement associated with $1.5 billion investment in the modernization program, while maintaining competitive rates for its shippers. The CCRM recovers the revenue requirement associated with qualifying modernization costs that Columbia Transmission incurs after satisfying the requirement associated with $100.0 million in annual capital maintenance expenditures. The CCRM applies to Columbia Transmission's transportation shippers. The CCRM will not exceed $300.0 million per year in investment in eligible facilities, subject to a 15% annual tolerance and a total cap of $1.5 billion for the entire five-year initial term.
	Chesapeake, Virginia LNG Facility Modernization. In connection with long-term extensions of their expiring service agreements, the three customers of Columbia Transmission's Chesapeake, Virginia LNG peaking facility agreed to fund upgrades to modernize the facility. Under the settlement, Columbia Transmission will invest approximately $30 million to upgrade the facility and each customer will extend its contract for 15 years. The settlement was filed with the FERC on February 28, 2013 and approved without modification on June 3, 2013. The project's first phase is scheduled to be complete in the fourth quarter of 2013.
	Cost Recovery Trackers. A significant portion of the transmission and storage regulated companies' revenue is related to the recovery of their operating costs, the review and recovery of which occurs via standard regulatory proceedings with the FERC under section 7 of the Natural Gas Act. However, certain operating costs of the NiSource regulated transmission and storage companies are significant and recurring in nature, such as fuel for compression and lost and unaccounted for gas. The FERC allows for the recovery of such costs via cost tracking mechanisms. These tracking mechanisms allow the transmission and storage companies' rates to fluctuate in response to changes in certain operating costs or conditions as they occur to facilitate the timely recovery of its costs incurred. The tracking mechanisms involve a rate adjustment that is filed at a predetermined frequency, typically annually, with the FERC and is subject to regulatory review before new rates go into effect. Other such costs under regulatory tracking mechanisms include upstream pipeline transmission, electric compression, environmental, and operational purchases and sales of natural gas.
	Electric Operations Regulatory Matters
	Significant Rate Developments. As part of a multi-state effort to strengthen the electric transmission system serving the Midwest, Northern Indiana anticipates making investments in two projects that were authorized by the MISO and are scheduled to be in service during the latter part of the decade. On July 19, 2012 and December 19, 2012, the FERC issued orders approving construction work in progress in rate base and abandoned plant cost recovery requested by Northern Indiana, for the 100-mile, 345 kV transmission project and its right to develop 50 percent of the 66-mile, 765 kV project. On December 19, 2012, the FERC issued an order authorizing Northern Indiana's request to transition to forward looking rates, allowing more timely recovery of Northern Indiana's investment in transmission assets. Northern Indiana began recording revenue in the first quarter of 2013 using a forward looking rate, based on an average construction work in progress balance of $19.8 million. For the nine months ended September 30, 2013 revenue of $2.3 million was recorded.
	On July 19, 2013, Northern Indiana filed its electric TDSIC, further discussed above, with the IURC. The filing included the seven year plan of eligible investments for a total of approximately $1.1 billion with the majority of the spend occurring in years 2016 through 2020. An order is expected by the first quarter of 2014.
	Cost Recovery and Trackers. A significant portion of Northern Indiana's revenue is related to the recovery of fuel costs to generate power and the fuel costs related to purchased power. These costs are recovered through a FAC, a standard, quarterly, “summary” regulatory proceeding in Indiana.
	Certain operating costs of the Electric Operations are significant, recurring in nature, and generally outside the control of Northern Indiana. The IURC allows for recovery of such costs via cost tracking mechanisms. Such tracking mechanisms allow for abbreviated regulatory proceedings in order for Northern Indiana to implement charges and recover appropriate costs. Tracking mechanisms allow for more timely recovery of such costs as compared with more traditional cost recovery mechanisms. Examples of such mechanisms include electric energy efficiency programs, MISO non-fuel costs and revenues, resource capacity charges, and environmental related costs.
	Northern Indiana has approval from the IURC to recover certain environmental related costs through an ECT. Under the ECT, Northern Indiana is permitted to recover (1) AFUDC and a return on the capital investment expended by Northern Indiana to implement environmental compliance plan projects through an ECRM and (2) related operation and maintenance and depreciation expenses once the environmental facilities become operational through an EERM.
	On October 10, 2013, the IURC issued an order approving Northern Indiana’s MATS Compliance Projects. Refer to Note 17-C, “Environmental Matters,” for additional information on the MATS rule. The Order approved estimated capital costs of $59.3 million and granted the requested ratemaking relief and accounting treatment associated with these projects through the annual EERM and semi-annual ECRM tracker filings.
	On April 24, 2013, the IURC issued an order on ECR-21 approving Northern Indiana's request to begin earning a return on net capital expenditures of $376.4 million. On August 1, 2013, Northern Indiana filed ECR-22 requesting a return on net capital expenditures of $478.8 million, an increase of $102.4 million from ECR-21.

Risk_Management_Activities

Risk Management Activities	9 Months Ended
	Sep. 30, 2013
Derivative Instruments and Hedges, Assets [Abstract]	'
Risk Management And Energy Marketing Activities	'
	Risk Management Activities
	NiSource is exposed to certain risks relating to its ongoing business operations. The primary risks managed by using derivative instruments are commodity price risk and interest rate risk. Derivative natural gas contracts are entered into to manage the price risk associated with natural gas price volatility and to secure forward natural gas prices. Interest rate swaps are entered into to manage interest rate risk or fair value risk associated with NiSource’s borrowings. NiSource designates some of its commodity forward contracts as cash flow hedges of forecasted purchases of commodities and designates its interest rate swaps as fair value hedges of fixed-rate borrowings. Additionally, certain NiSource subsidiaries enter into forward physical contracts with various third parties to procure or sell natural gas or power. Certain forward physical contracts are derivatives which qualify for, and for which NiSource may elect, the normal purchase and normal sales exception which do not require mark-to-market accounting.
	Accounting Policy for Derivative Instruments.    The ASC topic on accounting for derivatives and hedging requires an entity to recognize all derivatives as either assets or liabilities on the Condensed Consolidated Balance Sheets (unaudited) at fair value, unless such contracts are exempted, such as normal purchase and normal sale contracts under the provisions of the ASC topic. The accounting for changes in the fair value of a derivative depends on the intended use of the derivative and resulting designation.
	NiSource uses a variety of derivative instruments (exchange traded futures and options, physical forwards and options, commodity swaps, and interest rate swaps) to effectively manage its commodity price risk and interest rate risk exposure. If certain conditions are met, a derivative may be specifically designated as (a) a hedge of the exposure to changes in the fair value of a recognized asset or liability or an unrecognized firm commitment, or (b) a hedge of the exposure to variable cash flows of a forecasted transaction. In order for a derivative contract to be designated as a hedge, the relationship between the hedging instrument and the hedged item or transaction must be highly effective. The effectiveness test is performed at the inception of the hedge and each reporting period thereafter, throughout the period that the hedge is designated. Any amounts determined to be ineffective are recognized currently in earnings. For derivative contracts that qualify for the normal purchase and normal sales exception, a contract’s fair value is not recognized in the Condensed Consolidated Financial Statements (unaudited) until the contract is settled.
	Unrealized and realized gains and losses are recognized each period as components of AOCI, regulatory assets and liabilities or earnings depending on the designation of the derivative instrument and regulatory accounting treatment. For subsidiaries that utilize derivatives for cash flow hedges, the effective portions of the gains and losses are recorded to AOCI and are recognized in earnings concurrent with the disposition of the hedged risks. If a forecasted transaction corresponding to a cash flow hedge is no longer probable to occur, the accumulated gains or losses on the derivative are recognized currently in earnings. For fair value hedges, the gains and losses are recorded in earnings each period together with the change in the fair value of the hedged item. As a result of the rate-making process, the rate-regulated subsidiaries generally record gains and losses as regulatory liabilities or assets and recognize such gains or losses in earnings when both the contracts settle and the physical commodity flows. These gains and losses recognized in earnings are then subsequently recovered or passed back to customers in revenues through rates. When gains and losses are recognized in earnings, they are recognized in revenues or cost of sales for derivatives that correspond to commodity risk activities and are recognized in interest expense for derivatives that correspond to interest-rate risk activities.
	For its commodity price risk programs, NiSource has elected not to net the fair value amounts of its derivative instruments or the fair value amounts recognized for its right to receive or obligation to pay cash collateral arising from those derivative instruments recognized at fair value, which are executed with the same counterparty under a master netting arrangement. NiSource discloses amounts recognized for the right to reclaim cash collateral within “Restricted cash” and amounts recognized for the obligation to return cash collateral within “Other accruals” on the Condensed Consolidated Balance Sheets (unaudited).
	Commodity Price Risk Programs.    NiSource and NiSource’s utility customers are exposed to variability in cash flows associated with natural gas purchases and volatility in natural gas prices. NiSource purchases natural gas for sale and delivery to its retail, commercial and industrial customers, and for most customers the variability in the market price of gas is passed through in their rates. Some of NiSource’s utility subsidiaries offer programs where variability in the market price of gas is assumed by the respective utility. The objective of NiSource’s commodity price risk programs is to mitigate this gas cost variability, for NiSource or on behalf of its customers, associated with natural gas purchases or sales by economically hedging the various gas cost components by using a combination of futures, options, forward physical contracts or other derivative contracts. Northern Indiana also uses derivative contracts to minimize risk associated with power price volatility. These commodity price risk programs and their respective accounting treatment are described below.
	Northern Indiana, Columbia of Pennsylvania, Columbia of Kentucky and Columbia of Virginia use NYMEX futures and NYMEX options to minimize risk associated with gas price volatility. These derivative programs must be marked to fair value, but because these derivatives are used within the framework of the companies’ GCR or FAC mechanism, regulatory assets or liabilities are recorded to offset the change in the fair value of these derivatives.
	Northern Indiana and Columbia of Virginia offer a fixed price program as an alternative to the standard GCR mechanism. These services provide certain customers with the opportunity to either lock in their gas cost or place a cap on the gas costs that would be charged in future months. In order to hedge the anticipated physical purchases associated with these obligations, forward physical contracts, NYMEX futures and NYMEX options are used to secure forward gas prices. The accounting treatment elected for these contracts is varied in that certain of these contracts have been accounted for as cash flow hedges while some contracts are not. The accounting treatment is based on the election of the company. The normal purchase and normal sales exception is elected for forward physical contracts associated with these programs where delivery of the commodity is probable to occur.
	Northern Indiana also offers a DependaBill program to its customers as an alternative to the standard tariff rate that is charged to residential customers. The program allows Northern Indiana customers to fix their total monthly bill in future months at a flat rate regardless of gas usage or commodity cost. In order to hedge the anticipated physical purchases associated with these obligations, forward physical contracts, NYMEX futures and NYMEX options have been used to secure forward gas prices. The normal purchase and normal sales exception is elected for forward physical contracts associated with these programs where delivery of the commodity is probable to occur.
	Northern Indiana enters into gas purchase contracts at first of the month prices that give counterparties the daily option to either sell an additional package of gas at first of the month prices or recall the original volume to be delivered. Northern Indiana charges a fee for this option. The changes in the fair value of these options are primarily due to the changing expectations of the future intra-month volatility of gas prices. These written options are derivative instruments, must be marked to fair value and do not meet the requirement for hedge accounting treatment. However, Northern Indiana records the related gains and losses associated with these transactions as a regulatory asset or liability.
	Columbia of Kentucky, Columbia of Ohio and Columbia of Pennsylvania enter into contracts that allow counterparties the option to sell gas to them at first of the month prices for a particular month of delivery. These Columbia LDCs charge the counterparties a fee for this option. The changes in the fair value of the options are primarily due to the changing expectations of the future intra-month volatility of gas prices. These Columbia LDCs defer a portion of the change in the fair value of the options as either a regulatory asset or liability based on the regulatory customer sharing mechanisms in place, with the remaining changes in fair value recognized currently in earnings.
	As part of the MISO Day 2 initiative, Northern Indiana was allocated or has purchased FTRs. These FTRs help Northern Indiana offset congestion costs due to the MISO Day 2 activity. The FTRs are marked to fair value and are not accounted for as a hedge, but since congestion costs are recoverable through the fuel cost recovery mechanism, the related gains and losses associated with marking these derivatives to market are recorded as a regulatory asset or liability. In the second quarter of 2008, MISO changed its allocation procedures from an allocation of FTRs to an allocation of ARRs, whereby Northern Indiana was allocated ARRs based on its historical use of the MISO administered transmission system. ARRs entitle the holder to a stream of revenues or charges based on the price of the associated FTR in the FTR auction, so ARRs can be used to purchase FTRs in the FTR auction. ARRs are not derivatives.
	On September 1, 2013, NiSource sold the commercial and industrial natural gas portfolio of its unregulated natural gas marketing business. The sale included the physical contracts and associated financial hedges that comprise the portfolio, as well as the gas inventory and customer deposits of the business. The physical sales contracts marked-to-market had a fair value of approximately $35.4 million at December 31, 2012, while the financial derivative contracts marked-to-market had a fair value loss of $33.2 million at December 31, 2012. These amounts have been reclassified to held for sale as of December 31, 2012. Refer to Note 4, "Discontinued Operations and Assets and Liabilities Held for Sale" for additional information regarding the transaction.
	Commodity price risk program derivative contracted gross volumes are as follows:
		September 30, 2013			December 31, 2012
	Commodity Price Risk Program:
	Gas price volatility program derivatives (MMDth)	25.8			26.3
	Price Protection Service program derivatives (MMDth)	1			1.2
	DependaBill program derivatives (MMDth)	0.3			0.3
	Gas marketing program derivatives (MMDth)(1)(3)	—			9.1
	Gas marketing forward physical derivatives (MMDth)(2)(3)	—			8.4
	Electric energy program FTR derivatives (mw)	1,218.20			8,927.30
	(1) Basis contract volumes not included in the above table were 8.2 MMDth as of December 31, 2012.
	(2) Basis contract volumes not included in the above table were 9.2 MMDth as of December 31, 2012.
	(3) Contract volumes are from NiSource's unregulated natural gas marketing business that was sold on September 1, 2013.
	Interest Rate Risk Activities. NiSource recognizes that the prudent and selective use of derivatives may help it to lower its cost of debt capital and manage its interest rate exposure. NiSource Finance has entered into various “receive fixed” and “pay floating” interest rate swap agreements which modify the interest rate characteristics of a portion of its outstanding long-term debt from fixed to variable rate. These interest rate swaps also serve to hedge the fair market value of NiSource Finance’s outstanding debt portfolio. As of September 30, 2013, NiSource had $7.2 billion of outstanding fixed rate debt, of which $500 million is subject to fluctuations in interest rates as a result of the fixed-to-variable interest rate swap transactions. These interest rate swaps are designated as fair value hedges. NiSource had no net gain or loss recognized in earnings due to hedging ineffectiveness for the nine months ended September 30, 2013 and 2012.
	On July 22, 2003, NiSource Finance entered into fixed-to-variable interest rate swap agreements in a notional amount of $500 million with four counterparties which will expire on July 15, 2014. NiSource Finance receives payments based upon a fixed 5.40% interest rate and pays a floating interest amount based on U.S. 6-month BBA LIBOR plus an average of 0.78% per annum. There was no exchange of premium at the initial date of the swaps.
	Contemporaneously with the issuance on September 16, 2005 of $1 billion of its 5.25% and 5.45% notes, maturing September 15, 2017 and 2020, respectively, NiSource Finance settled $900 million of forward starting interest rate swap agreements with six counterparties. NiSource paid an aggregate settlement payment of $35.5 million which is being amortized from AOCI to interest expense over the term of the underlying debt, resulting in an effective interest rate of 5.67% and 5.88%, respectively. As of September 30, 2013, AOCI includes $8.6 million related to forward starting interest rate swap settlement, net of tax. These derivative contracts are accounted for as a cash flow hedge.
	As of September 30, 2013, NiSource holds a 47.5% interest in Millennium. As NiSource reports Millennium as an equity method investment, NiSource is required to recognize a proportional share of Millennium’s OCI. NiSource’s proportionate share of the remaining unrecognized loss associated with settled interest rate swaps is $17.9 million, net of tax, as of September 30, 2013. Millennium is amortizing the losses related to these terminated interest rate swaps into earnings using the effective interest method through interest expense as interest payments are made. NiSource records its proportionate share of the amortization as Equity Earnings in Unconsolidated Affiliates in the Condensed Statements of Consolidated Income (unaudited).
	NiSource’s location and fair value of derivative instruments on the Condensed Consolidated Balance Sheets (unaudited) were:
	Asset Derivatives (in millions)	September 30,				December 31,
		2013				2012
	Balance Sheet Location	Fair Value				Fair Value
	Derivatives designated as hedging instruments
	Interest rate risk activities
	Price risk management assets (current)	$	21			$	—
	Price risk management assets (noncurrent)	—				40.4
	Total derivatives designated as hedging instruments	$	21			$	40.4
	Derivatives not designated as hedging instruments
	Commodity price risk programs
	Price risk management assets (current)	$	0.1			$	0.5
	Price risk management assets (noncurrent)	—				0.3
	Assets held for sale (current)(1)	—				107
	Total derivatives not designated as hedging instruments	$	0.1			$	107.8
	Total Asset Derivatives	$	21.1			$	148.2
	(1) Prior to the classification as "Assets held for sale," $15.3 million was classified as noncurrent.
	Liability Derivatives (in millions)	September 30,				December 31,
		2013				2012
	Balance Sheet Location	Fair Value				Fair Value
	Derivatives designated as hedging instruments
	Commodity price risk programs
	Price risk management liabilities (current)	$	0.1			$	0.1
	Price risk management liabilities (noncurrent)	—				—
	Total derivatives designated as hedging instruments	$	0.1			$	0.1
	Derivatives not designated as hedging instruments
	Commodity price risk programs
	Price risk management liabilities (current)	$	8.7			$	8.1
	Price risk management liabilities (noncurrent)	1.5				2.6
	Liabilities held for sale (current)(2)	—				104.7
	Total derivatives not designated as hedging instruments	$	10.2			$	115.4
	Total Liability Derivatives	$	10.3			$	115.5
	(2) Prior to the classification as "Liabilities held for sale," $17.7 million was classified as noncurrent.
As noted in NiSource's accounting policy for derivative instruments, above, for its commodity price risk programs, NiSource has elected not to net fair value amounts for its derivative instruments or the fair value amounts recognized for its right to receive cash collateral or obligation to pay cash collateral arising from those derivative instruments recognized at fair value, which are executed with the same counterparty under a master netting arrangement.
The tables below represent the amounts subject to an enforceable master netting arrangement not otherwise disclosed:
Offsetting of Derivative Assets (in millions)
As of September 30, 2013
	Gross Amounts of Recognized Assets				Gross Amounts Offset in the Statement of Financial Position				Net Amounts of Assets Presented in the Statement of Financial Position				Gross Amounts Not Offset in the Statement in the Statement of Financial Position				Net Amount
Counterparty A (1)	$	—			$	—			$	—			$	—			$	—
Counterparty B	0.1				—				0.1				(10.3		)		(10.2		)
Other (2)	21				—				21				—				21
Total	$	21.1			$	—			$	21.1			$	(10.3	)		$	10.8
Offsetting of Derivative Liabilities (in millions)
As of September 30, 2013
	Gross Amounts of Recognized Liabilities				Gross Amounts Offset in the Statement of Financial Position				Net Amounts of Liabilities Presented in the Statement of Financial Position				Gross Amounts Not Offset in the Statement in the Statement of Financial Position				Net Amount
Counterparty A (1)	$	—			$	—			$	—			$	—			$	—
Counterparty B	(10.3		)		—				(10.3		)		10.3				—
Other (2)	—				—				—				—				—
Total	$	(10.3	)		$	—			$	(10.3	)		$	10.3			$	—
Offsetting of Derivative Assets (in millions)
As of December 31, 2012
	Gross Amounts of Recognized Assets				Gross Amounts Offset in the Statement of Financial Position				Net Amounts of Assets Presented in the Statement of Financial Position				Gross Amounts Not Offset in the Statement in the Statement of Financial Position				Net Amount
Counterparty A (1)	$	71.8			$	—			$	71.8			$	(71.8	)		$	—
Counterparty B	0.9				—				0.9				(0.9		)		—
Other (2)	75.5				—				75.5				—				75.5
Total	$	148.2			$	—			$	148.2			$	(72.7	)		$	75.5
Offsetting of Derivative Liabilities (in millions)
As of December 31, 2012
	Gross Amounts of Recognized Liabilities				Gross Amounts Offset in the Statement of Financial Position				Net Amounts of Liabilities Presented in the Statement of Financial Position				Gross Amounts Not Offset in the Statement in the Statement of Financial Position				Net Amount
Counterparty A (1)	$	(103.4	)		$	—			$	(103.4	)		$	71.8			$	(31.6	)
Counterparty B	(10.8		)		—				(10.8		)		0.9				(9.9		)
Other (2)	(1.3		)		—				(1.3		)		—				(1.3		)
Total	$	(115.5	)		$	—			$	(115.5	)		$	72.7			$	(42.8	)
(1) Amounts in "Counterparty A" are balances from the commercial and industrial natural gas portfolio of NiSource's unregulated natural gas marketing business which was sold on September 1, 2013, and are included in assets and liabilities held for sale. Refer to Note 4, "Discontinued Operations and Assets and Liabilities Held for Sale" for additional information regarding the transaction.
(2) Amounts in "Other" include physical positions with counterparties that are part of NiSource's unregulated natural gas marketing business as well as fixed-to-variable interest rate swap agreements entered into by NiSource.
The effect of derivative instruments on the Condensed Statements of Consolidated Income (unaudited) was:
Derivatives in Cash Flow Hedging Relationships
Three Months Ended (in millions)
	Amount of Gain								Location of Loss		Amount of Loss
	Recognized in OCI on								Reclassified from  AOCI		Reclassified from AOCI
	Derivative (Effective								into Income (Effective		into Income (Effective
	Portion)								Portion)		Portion)
Derivatives in Cash Flow	September 30,				September 30, 2012						September 30,				September 30, 2012
Hedging Relationships	2013										2013
Commodity price risk programs	$	—			$	0.2			Cost of Sales		$	—			$	—
Interest rate risk activities	—				0.4				Interest expense, net		(0.4		)		(0.7		)
Total	$	—			$	0.6					$	(0.4	)		$	(0.7	)
Nine Months Ended (in millions)
	Amount of Gain								Location of Gain  (Loss)		Amount of Gain (Loss)
	Recognized in OCI on								Reclassified from  AOCI		Reclassified from AOCI
	Derivative (Effective								into Income (Effective		into Income (Effective
	Portion)								Portion)		Portion)
Derivatives in Cash Flow	September 30,				September 30, 2012						September 30,				September 30, 2012
Hedging Relationships	2013										2013
Commodity price risk programs	$	—			$	0.8			Cost of Sales		$	0.1			$	(0.8	)
Interest rate risk activities	—				1.2				Interest expense, net		(1.2		)		(2.0		)
Total	$	—			$	2					$	(1.1	)		$	(2.8	)
There was no income statement recognition of gains or losses for the ineffective portion and amounts excluded from effectiveness testing for derivatives in cash flow hedging relationships for the three and nine months ended September 30, 2013 and 2012.
It is anticipated that during the next twelve months the expiration and settlement of cash flow hedge contracts will result in income statement recognition of amounts currently classified in AOCI of approximately $0.1 million of loss, net of taxes.
Derivatives in Fair Value Hedging Relationships
Three Months Ended (in millions)
Derivatives in Fair Value Hedging	Location of Loss Recognized in		Amount of Loss Recognized
Relationships	Income on Derivatives		in Income on Derivatives
			September 30, 2013				September 30, 2012
Interest rate risk activities	Interest expense, net		$	(9.9	)		$	(8.3	)
Total			$	(9.9	)		$	(8.3	)
Nine Months Ended (in millions)
Derivatives in Fair Value Hedging	Location of Loss Recognized in		Amount of Loss Recognized
Relationships	Income on Derivatives		in Income on Derivatives
			September 30, 2013				September 30, 2012
Interest rate risk activities	Interest expense, net		$	(19.4	)		$	(16.5	)
Total			$	(19.4	)		$	(16.5	)
Three Months Ended (in millions)
Hedged Item in Fair Value Hedge	Location of Gain Recognized in		Amount of Gain Recognized
Relationships	Income on Related Hedged Item		in Income on Related Hedged Items
			September 30, 2013				September 30, 2012
Fixed-rate debt	Interest expense, net		$	9.9			$	8.3
Total			$	9.9			$	8.3
Nine Months Ended (in millions)
Hedged Item in Fair Value Hedge	Location of Gain Recognized in		Amount of Gain Recognized
Relationships	Income on Related Hedged Item		in Income on Related Hedged Items
			September 30, 2013				September 30, 2012
Fixed-rate debt	Interest expense, net		$	19.4			$	16.5
Total			$	19.4			$	16.5
Derivatives not designated as hedging instruments
Three Months Ended (in millions)
Derivatives Not Designated as Hedging	Location of Gain (Loss)		Amount of Realized/Unrealized Gain
Instruments	Recognized in		(Loss) Recognized in Income on
	Income on Derivatives		Derivatives *
			September 30, 2013				September 30, 2012
Commodity price risk programs	Gas Distribution revenues		$	—			$	—
Commodity price risk programs	Other revenues		—				—
Commodity price risk programs	Cost of Sales		6.6				6.8
Commodity price risk programs	(Loss) Income from Discontinued Operations - net of taxes		(1.2		)		0.6
Total			$	5.4			$	7.4
* For the amounts of realized/unrealized gain (loss) recognized in income on derivatives disclosed in the table above, gains of $6.7 million and $6.8 million for the three months ended September 30, 2013 and 2012, respectively, were deferred as allowed per regulatory orders. These amounts will be amortized to income over future periods of up to twelve months as specified in a regulatory order.
Nine Months Ended (in millions)
Derivatives Not Designated as Hedging	Location of Gain (Loss)		Amount of Realized/Unrealized Gain
Instruments	Recognized in		(Loss) Recognized in Income on
	Income on Derivatives		Derivatives *
			September 30, 2013				September 30, 2012
Commodity price risk programs	Gas Distribution revenues		$	—			$	0.3
Commodity price risk programs	Other revenues		—				—
Commodity price risk programs	Cost of Sales		7.5				(8.6		)
Commodity price risk programs	(Loss) Income from Discontinued Operations - net of taxes		(0.8		)		2.8
Total			$	6.7			$	(5.5	)
* For the amounts of realized/unrealized gain (loss) recognized in income on derivatives disclosed in the table above, a gain of $7.6 million for the nine months ended September 30, 2013 and a loss of $8.3 million for the nine months ended 2012 were deferred as allowed per regulatory orders. These amounts will be amortized to income over future periods of up to twelve months as specified in a regulatory order.
NiSource’s derivative instruments measured at fair value as of September 30, 2013 and December 31, 2012 do not contain any credit-risk-related contingent features.
Certain NiSource affiliates have physical commodity purchase agreements that contain “ratings triggers” that require increases in collateral if the credit rating of NiSource or certain of its affiliates are rated below BBB- by Standard & Poor’s or below Baa3 by Moody’s. These agreements are primarily for the physical purchase or sale of natural gas and electricity. The collateral requirement from a downgrade below the ratings trigger levels would amount to approximately $0.8 million. In addition to agreements with ratings triggers, there are some agreements that contain “adequate assurance” or “material adverse change” provisions that could result in additional credit support such as letters of credit and cash collateral to transact business.
NiSource had $13.5 million and $45.7 million of cash on deposit with brokers for margin requirements associated with open derivative positions reflected within “Restricted cash” on the Condensed Consolidated Balance Sheets (unaudited) as of September 30, 2013 and December 31, 2012, respectively.

Fair_Value_Disclosures

Fair Value Disclosures	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Disclosures	'
	Fair Value Disclosures
	A.    Fair Value Measurements
	Recurring Fair Value Measurements. The following tables present financial assets and liabilities measured and recorded at fair value on NiSource’s Condensed Consolidated Balance Sheets (unaudited) on a recurring basis and their level within the fair value hierarchy as of September 30, 2013 and December 31, 2012:
	Recurring Fair Value Measurements	Quoted Prices in		Significant		Significant			Balance as of September 30, 2013
	September 30, 2013 (in millions)	Active Markets		Other		Unobservable
		for Identical		Observable		Inputs
		Assets		Inputs		(Level 3)
		(Level 1)		(Level 2)
	Assets
	Commodity Price risk management assets:
	Physical price risk programs	$	—	$	—	$	—		$	—
	Financial price risk programs	0.1				—			0.1
	Interest rate risk activities	—		21		—			21
	Available-for-sale securities	26.5		99.9		—			126.4
	Total	$	26.6	$	120.9	$	—		$	147.5
	Liabilities
	Commodity Price risk management liabilities:
	Physical price risk programs	$	—	$	—	$	—		$	—
	Financial price risk programs	9.7		—		0.6			10.3
	Total	$	9.7	$	—	$	0.6		$	10.3
	Recurring Fair Value Measurements	Quoted Prices in		Significant		Significant			Balance as of
	December 31, 2012 (in millions)	Active Markets		Other		Unobservable			December 31, 2012
		for Identical		Observable		Inputs
		Assets		Inputs		(Level 3)
		(Level 1)		(Level 2)
	Assets
	Commodity Price risk management assets:
	Physical price risk programs	$	—	$	—	$	—		$	—
	Physical price risk programs (assets held for sale)	—		35.4		—			35.4
	Financial price risk programs	0.7		—		0.1			0.8
	Financial price risk programs (assets held for sale)	70.8		0.8		—			71.6
	Interest rate risk activities	—		40.4		—			40.4
	Available-for-sale securities	27.4		84.4		—			111.8
	Total	$	98.9	$	161	$	0.1		$	260
	Liabilities
	Commodity Price risk management liabilities:
	Physical price risk programs	$	—	$	—	$	—		$	—
	Financial price risk programs	10.8		—		—			10.8
	Financial price risk programs (liabilities held for sale)	104.2		0.5		—			104.7
	Total	$	115	$	0.5	$	—		$	115.5
	Price risk management assets and liabilities include commodity exchange-traded and non-exchange-based derivative contracts. Exchange-traded derivative contracts are based on unadjusted quoted prices in active markets and are classified within Level 1. These financial assets and liabilities are secured with cash on deposit with the exchange; therefore nonperformance risk has not been incorporated into these valuations. Certain non-exchange-traded derivatives are valued using broker or over-the-counter, on-line exchanges. In such cases, these non-exchange-traded derivatives are classified within Level 2. Non-exchange-based derivative instruments include swaps, forwards, and options. In certain instances, these instruments may utilize models to measure fair value. NiSource uses a similar model to value similar instruments. Valuation models utilize various inputs that include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, other observable inputs for the asset or liability, and market-corroborated inputs, i.e., inputs derived principally from or corroborated by observable market data by correlation or other means. Where observable inputs are available for substantially the full term of the asset or liability, the instrument is categorized in Level 2. Certain derivatives trade in less active markets with a lower availability of pricing information and models may be utilized in the valuation. When such inputs have a significant impact on the measurement of fair value, the instrument is categorized in Level 3. Credit risk is considered in the fair value calculation of derivative instruments that are not exchange-traded. Credit exposures are adjusted to reflect collateral agreements which reduce exposures. As of September 30, 2013 and December 31, 2012, there were no material transfers between fair value hierarchies. Additionally, there were no changes in the method or significant assumptions used to estimate the fair value of NiSource’s financial instruments.
	Price risk management assets also include fixed-to-floating interest-rate swaps, which are designated as fair value hedges, as a means to achieve NiSource’s targeted level of variable-rate debt as a percent of total debt. NiSource uses a calculation of future cash inflows and estimated future outflows related to the swap agreements, which are discounted and netted to determine the current fair value. Additional inputs to the present value calculation include the contract terms, as well as market parameters such as current and projected interest rates and volatility. As they are based on observable data and valuations of similar instruments, the interest-rate swaps are categorized in Level 2 in the fair value hierarchy. Credit risk is considered in the fair value calculation of the interest rate swap.
	Available-for-sale securities are investments pledged as collateral for trust accounts related to NiSource’s wholly-owned insurance company. Available-for-sale securities are included within “Other investments” in the Condensed Consolidated Balance Sheets (unaudited). Securities classified within Level 1 include U.S. Treasury debt securities which are highly liquid and are actively traded in over-the-counter markets. NiSource values corporate and mortgage-backed debt securities using a matrix pricing model that incorporates market-based information. These securities trade less frequently and are classified within Level 2. Total gains and losses from available-for-sale securities are included in other comprehensive income (loss). The amortized cost, gross unrealized gains and losses, and fair value of available-for-sale debt securities at September 30, 2013 and December 31, 2012 were:
	(in millions)	Amortized		Gross Unrealized Gains		Gross Unrealized Losses			Fair
		Cost							Value
	Available-for-sale debt securities, September 30, 2013
	U.S. Treasury	$	31.3	$	0.5	$	(0.3	)	$	31.5
	Corporate/Other	94.8		1.2		(1.1		)	94.9
	Total Available-for-sale debt securities	$	126.1	$	1.7	$	(1.4	)	$	126.4
	(in millions)	Amortized		Gross Unrealized Gains		Gross Unrealized Losses			Fair
		Cost							Value
	Available-for-sale debt securities, December 31, 2012
	U.S. Treasury	$	31.1	$	1.5	$	—		$	32.6
	Corporate/Other	76.8		2.5		(0.1		)	79.2
	Total Available-for-sale debt securities	$	107.9	$	4	$	(0.1	)	$	111.8
	For the three months ended September 30, 2013 and 2012, the net realized gain on the sale of available-for-sale U.S. Treasury debt securities was $0.1 million and zero, respectively. For the three months ended September 30, 2013 and 2012, the net realized gain on sale of available-for-sale Corporate/Other bond debt securities was zero and $0.1 million, respectively.
	For the nine months ended September 30, 2013 and 2012, the net realized gain on the sale of available-for-sale U.S. Treasury debt securities was $0.5 million and $0.3 million, respectively. For the nine months ended September 30, 2013 and 2012, the net realized gain on sale of available-for-sale Corporate/Other bond debt securities was $0.3 million and $0.1 million, respectively.
	The cost of maturities sold is based upon specific identification. At September 30, 2013, approximately $0.4 million of U.S. Treasury debt securities have maturities of less than a year while the remaining securities have maturities of greater than one year. At September 30, 2013, approximately $3.0 million of Corporate/Other bonds have maturities of less than a year while the remaining securities have maturities of greater than one year.
	There are no material items in the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis for the three and nine months ended September 30, 2013 and 2012.
	Non-recurring Fair Value Measurements. In January 2013, NiSource sold the service plan and leasing business lines of its Retail Services business. The disposed business lines were included in the Columbia Distribution Operations reporting unit and the Northern Indiana Gas Distribution Operations reporting unit. Goodwill associated with the disposed business lines was included in the carrying amount of the business lines in determining the gain on disposal. The amount of the goodwill included in the carrying amount was based on the relative fair values of the business lines disposed of and the portion of the reporting units that were retained. The fair value of the disposed business lines was determined by using the selling price of the business lines. The fair value of the reporting units that were retained was determined by a weighted average of income and market approaches. This approach was similar to the process undertaken to calculate the fair value of the reporting units for the goodwill impairment test conducted on May 1, 2012. These approaches are further discussed in NiSource’s Annual Report on Form 10-K for the fiscal year ended December 31, 2012 and yield fair values considered to be at Level 3 of the fair value hierarchy. The respective fair value of the disposed business lines was divided by the fair value of the reporting units to which the disposed business lines belonged. These percentages were then applied to those goodwill balances to determine their allocations. As a result of these procedures, NiSource recorded a disposal of goodwill of approximately $11.0 million during the first quarter of 2013. This amount is included within the "(Loss) Gain on Disposition of Discontinued Operations - net of taxes" on the Condensed Statements of Consolidated Income (unaudited).
	There were no significant non-recurring fair value measurements recorded during the nine months ended September 30, 2012.
	B.    Other Fair Value Disclosures for Financial Instruments. The carrying amount of cash and cash equivalents, restricted cash, notes receivable, customer deposits and short-term borrowings is a reasonable estimate of fair value due to their liquid or short-term nature. NiSource’s long-term borrowings are recorded at historical amounts unless designated as a hedged item in a fair value hedge.
	The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate fair value.
Long-term Debt. The fair values of these securities are estimated based on the quoted market prices for the same or similar issues or on the rates offered for securities of the same remaining maturities. Certain premium costs associated with the early settlement of long-term debt are not taken into consideration in determining fair value. These fair value measurements are classified as Level 2 within the fair value hierarchy. For the nine months ended September 30, 2013 and 2012, there were no changes in the method or significant assumptions used to estimate the fair value of the financial instruments.
The carrying amount and estimated fair values of financial instruments were as follows:
(in millions)	Carrying		Estimated Fair		Carrying			Estimated Fair
	Amount as of		Value as of		Amount as of			Value as of
	September 30, 2013		September 30, 2013		Dec. 31, 2012			Dec. 31, 2012
Long-term debt (including current portion)	$	7,630.30	$	8,172.10	$	7,326.30		$	8,389.00

Transfers_Of_Financial_Assets

Transfers Of Financial Assets	9 Months Ended
	Sep. 30, 2013
Transfers and Servicing [Abstract]	'
Transfers Of Financial Assets	'
	Transfers of Financial Assets
	Transfers of accounts receivable are accounted for as secured borrowings resulting in the recognition of short-term borrowings on the Condensed Consolidated Balance Sheets (unaudited). The maximum amount of debt that can be recognized related to NiSource’s accounts receivable programs is $515 million.
	All accounts receivable sold to the commercial paper conduits are valued at face value, which approximates fair value due to their short-term nature. The amount of the undivided percentage ownership interest in the accounts receivable sold is determined in part by required loss reserves under the agreements. Below is information about the accounts receivable securitization agreements entered into by NiSource’s subsidiaries.
	On October 23, 2009, Columbia of Ohio entered into an agreement to sell, without recourse, substantially all of its trade receivables, as they originate, to CGORC, a wholly-owned subsidiary of Columbia of Ohio. CGORC, in turn, is party to an agreement with BTMU and BNS, entered into on October 19, 2012, under the terms of which it sells an undivided percentage ownership interest in its accounts receivable to commercial paper conduits sponsored by BTMU and BNS. This agreement with BTMU and BNS was renewed on October 18, 2013. Prior to this agreement with BTMU and BNS, CGORC was party to a series of agreements with BTMU and RBS which dated from October 23, 2009 until its amendment on October 19, 2012. The maximum seasonal program limit under the terms of the new agreement remains at $240 million. The current agreement expires on October 17, 2014, and can be renewed if mutually agreed to by all parties. As of September 30, 2013, $73.3 million of accounts receivable had been transferred by CGORC. CGORC is a separate corporate entity from NiSource and Columbia of Ohio, with its own separate obligations, and upon a liquidation of CGORC, CGORC’s obligations must be satisfied out of CGORC’s assets prior to any value becoming available to CGORC’s stockholder.
	On October 23, 2009, Northern Indiana entered into an agreement to sell, without recourse, substantially all of its trade receivables, as they originate, to NARC, a wholly-owned subsidiary of Northern Indiana. NARC, in turn, is party to an agreement with PNC and Mizuho entered into on August 29, 2012, under the terms of which it sells an undivided percentage ownership interest in its accounts receivable to commercial paper conduits sponsored by PNC and Mizuho. This agreement with PNC and Mizuho was renewed on August 28, 2013. Prior to this agreement with PNC and Mizuho, NARC was party to a series of agreements with RBS which dated from October 23, 2009 until its amendment on August 29, 2012. The maximum seasonal program limit under the terms of the current agreement, which expires on August 27, 2014, is $200 million, and can be further renewed if mutually agreed to by all parties. As of September 30, 2013, $125.0 million of accounts receivable had been transferred by NARC. NARC is a separate corporate entity from NiSource and Northern Indiana, with its own separate obligations, and upon a liquidation of NARC, NARC’s obligations must be satisfied out of NARC’s assets prior to any value becoming available to NARC’s stockholder.
	On March 15, 2010, Columbia of Pennsylvania entered into an agreement to sell, without recourse, substantially all of its trade receivables, as they originate, to CPRC, a wholly-owned subsidiary of Columbia of Pennsylvania. CPRC, in turn, is party to an agreement with BTMU, also dated March 15, 2010, under the terms of which it sells an undivided percentage ownership interest in its accounts receivable to a commercial paper conduit sponsored by BTMU. The maximum seasonal program limit under the terms of the agreement is $75 million. On March 13, 2013, the agreement was renewed, having a new scheduled termination date of March 12, 2014, and can be further renewed if mutually agreed to by both parties. As of September 30, 2013, $10.0 million of accounts receivable had been transferred by CPRC. CPRC is a separate corporate entity from NiSource and Columbia of Pennsylvania, with its own separate obligations, and upon a liquidation of CPRC, CPRC’s obligations must be satisfied out of CPRC’s assets prior to any value becoming available to CPRC’s stockholder.
	The following table reflects the gross and net receivables transferred as well as short-term borrowings related to the securitization transactions as of September 30, 2013 and December 31, 2012 for Columbia of Ohio, Northern Indiana and Columbia of Pennsylvania:
	(in millions)	September 30, 2013		31-Dec-12
	Gross Receivables	$	350.8	$	525.3
	Less: Receivables not transferred	142.5		292
	Net receivables transferred	$	208.3	$	233.3
	Short-term debt due to asset securitization	$	208.3	$	233.3
	For both the three months ended September 30, 2013 and 2012, $0.5 million of fees associated with the securitization transactions were recorded as interest expense. For the nine months ended September 30, 2013 and 2012, fees of $2.0 million and $2.5 million associated with the securitization transactions were recorded as interest expense, respectively. Columbia of Ohio, Northern Indiana and Columbia of Pennsylvania remain responsible for collecting on the receivables securitized and the receivables cannot be sold to another party.

Goodwill_Assets

Goodwill Assets	9 Months Ended
	Sep. 30, 2013
Goodwill And Other Intangible Assets [Abstract]	'
Goodwill And Other Intangible Assets	'
	Goodwill Assets
	In accordance with the provisions for goodwill accounting under GAAP, NiSource tests its goodwill for impairment annually as of May 1 each year unless indicators, events, or circumstances would require an immediate review. Goodwill is tested for impairment at a level of reporting referred to as a reporting unit, which generally is an operating segment or a component of an operating segment as defined by the FASB. NiSource's three reporting units are Columbia Distribution Operations, Columbia Transmission Operations and Northern Indiana Gas Distribution Operations.
	NiSource's goodwill assets as of September 30, 2013 were $3.7 billion pertaining primarily to the acquisition of Columbia on November 1, 2000. Of this amount, approximately $2.0 billion is allocated to Columbia Transmission Operations and $1.7 billion is allocated to Columbia Distribution Operations. In addition, Northern Indiana Gas Distribution Operations' goodwill assets at September 30, 2013 related to the purchase of Northern Indiana Fuel and Light in March 1993 and Kokomo Gas in February 1992 were $17.8 million.
	NiSource completed a quantitative ("step 1") fair value measurement of its reporting units during the May 1, 2012 goodwill test. The test indicated that the fair value of each of the reporting units that carry or are allocated goodwill substantially exceeded their carrying values, indicating that no impairment existed under the step 1 annual impairment test.
	In September 2011, FASB issued Accounting Standards Update 2011-08, which allows entities testing goodwill for impairment the option of performing a qualitative ("step 0") assessment before calculating the fair value of a reporting unit for the goodwill impairment test. If a step 0 assessment is performed, an entity is no longer required to calculate the fair value of a reporting unit unless the entity determines that based on the qualitative step 0 assessment that it is more likely than not that its fair value is less than its carrying amount. The update was effective for fiscal years, and interim periods within those years, beginning after December 15, 2011.
	NiSource applied this guidance for its 2013 annual test and utilized the qualitative step 0 analysis to its reporting units for the annual impairment test performed as of May 1, 2013.
	For the current year qualitative step 0 test performed as of May 1, 2013, NiSource assessed various assumptions, events and circumstances that would have affected the estimated fair value of the reporting units in its base line May 1, 2012 test. The results of this assessment indicated that it is not more likely than not that its reporting unit fair values are less than the reporting unit carrying values and no impairments are necessary.
	NiSource considered whether there were any events or changes in circumstances subsequent to the annual test that would reduce the fair value of any of the reporting units below their carrying amounts and necessitate another goodwill impairment test. No such indicators were noted that would require a subsequent goodwill impairment testing during the third quarter.
	During the first quarter of 2013, as part of the sale of the service plan and leasing business lines of its Retail Services business, NiSource allocated $10.0 million of goodwill from Columbia Distribution Operations to the sale and allocated $1.0 million of goodwill from Northern Indiana Gas Distribution Operations to the sale. Refer to Note 4 "Discontinued Operations and Assets and Liabilities Held for Sale" for more information.

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes
	NiSource’s interim effective tax rates reflect the estimated annual effective tax rates for 2013 and 2012, adjusted for tax expense associated with certain discrete items. The effective tax rates for the three months ended September 30, 2013 and 2012 were 36.0% and 35.7%, respectively. The effective tax rates for the nine months ended September 30, 2013 and 2012 were 34.7% and 34.8%, respectively. These effective tax rates differ from the Federal tax rate of 35% primarily due to the effects of tax credits, state income taxes, utility rate-making, and other permanent book-to-tax differences.
	On January 2, 2013, the President signed into law the American Taxpayer Relief Act of 2012 (ATRA). ATRA, among other things, extends retroactively the research credit under Internal Revenue Code section 41 until December 31, 2013, and also extends and modifies 50% bonus depreciation for 2013. In general, 50% bonus depreciation will be available for property placed in service before January 1, 2014, or in the case of certain property having longer production periods, before January 1, 2015. NiSource recorded the effects of ATRA in the first quarter 2013. The retroactive extension of the research credit did not have a significant effect on net income.
	On March 7, 2013, the Congressional Joint Committee on Taxation took no exception to the conclusions reached by the IRS in its 2008-2010 audit examination of NiSource. Therefore, in the first quarter of 2013, NiSource recognized a federal income tax receivable of $15.9 million that was related to the 2008 and 2009 tax years and increases in net operating loss carryforwards of $0.6 million that was related to uncertain tax positions in the 2010-2012 tax years. NiSource received payments of $75.1 million in March 2013 and $70.6 million in April 2013 of principal and interest from the IRS related to the audit examination. The recognition of the receivables and net operating loss carryforwards did not materially affect tax expense or net income.
	On July 24, 2013, Transportation Finance Bill H3535 which was passed by the Massachusetts legislature, repealed the reduced tax rate of 6.5% for public utility corporations contained in Section 52A of Chapter 63 of the Massachusetts General Laws. Effective January 1, 2014, Columbia of Massachusetts will be taxed at 8.0%, which is the current franchise tax rate for corporations that are not public utilities. Deferred income taxes were adjusted by $3.2 million as a result of this law change.
	On September 13, 2013, the IRS and U.S. Treasury issued final regulations on the deductibility and capitalization of expenditures related to tangible property, generally effective for tax years beginning on or after January 1, 2014. Taxpayers may elect early adoption of the regulations for the 2012 or 2013 tax year. NiSource does not plan to early adopt the regulations. Deferred tax liabilities at September 30, 2013 are not materially affected by the regulations. The final regulations do not impact the effect of Revenue Procedure 2013-24 issued on April 30, 2013 which provided guidance for repairs related to generation property. Among other things, the Revenue Procedure listed units of property and material components of units of property for purposes of analyzing repair versus capitalization issues. NiSource will likely adopt this Revenue Procedure for income tax filings in 2014.
	There were no material changes recorded in the third quarter of 2013 to NiSource's uncertain tax positions as of December 31, 2012.

Pension_And_Other_Postretireme

Pension And Other Postretirement Benefits	9 Months Ended
	Sep. 30, 2013
Pension and Other Postretirement Benefit Expense [Abstract]	'
Pension And Other Postretirement Benefits	'
	Pension and Other Postretirement Benefits
	NiSource provides defined contribution plans and noncontributory defined benefit retirement plans that cover its employees. Benefits under the defined benefit retirement plans reflect the employees’ compensation, years of service and age at retirement. Additionally, NiSource provides health care and life insurance benefits for certain retired employees. The majority of employees may become eligible for these benefits if they reach retirement age while working for NiSource. The expected cost of such benefits is accrued during the employees’ years of service. Current rates of rate-regulated companies include postretirement benefit costs, including amortization of the regulatory assets that arose prior to inclusion of these costs in rates. For most plans, cash contributions are remitted to grantor trusts.
	For the nine months ended September 30, 2013, NiSource has contributed $9.1 million to its pension plans and $29.6 million to its other postretirement benefit plans.
	The following tables provide the components of the plans’ net periodic benefits cost for the three and nine months ended September 30, 2013 and 2012:
		Pension Benefits								Other Postretirement
										Benefits
	Three Months Ended September 30, (in millions)	2013				2012				2013			2012
	Components of Net Periodic Benefit Cost
	Service cost	$	9			$	9.4			$	3		$	2.8
	Interest cost	24.9				28.2				8			9.6
	Expected return on assets	(42.0		)		(41.2		)		(7.6		)	(6.7		)
	Amortization of transition obligation	—				—				0.2			0.3
	Amortization of prior service cost	—				0.1				(0.2		)	0.5
	Recognized actuarial loss	18.9				20.3				2.8			2.3
	Settlement loss	4				1.9				—			—
	Total Net Periodic Benefit Costs	$	14.8			$	18.7			$	6.2		$	8.8
		Pension Benefits								Other Postretirement
										Benefits
	Nine Months Ended September 30, (in millions)	2013				2012				2013			2012
	Components of Net Periodic Benefit Cost
	Service cost	$	27.7			$	28.2			$	9		$	8.4
	Interest cost	73.5				84.6				24.2			28.2
	Expected return on assets	(126.5		)		(123.4		)		(22.8		)	(20.1		)
	Amortization of transition obligation	—				—				0.4			0.9
	Amortization of prior service cost	0.2				0.3				(0.6		)	0.3
	Recognized actuarial loss	59.3				60.9				8.4			7.1
	Settlement loss	28.3				1.9				—			—
	Total Net Periodic Benefit Costs	$	62.5			$	52.5			$	18.6		$	24.8
	For the quarters ended September 30, 2013 and 2012, pension and other postretirement benefit cost of approximately $4.4 million and $8.2 million, respectively, was capitalized as a component of plant or recognized as a regulatory asset or liability consistent with regulatory orders for certain of NiSource’s regulated businesses. For the nine months ended September 30, 2013 and 2012, pension and other postretirement benefit cost of approximately $30.2 million and $19.1 million, respectively, was capitalized as a component of plant or recognized as a regulatory asset or liability consistent with regulatory orders for certain of NiSource's regulated businesses.
	As of February 28, 2013, it became probable that a NiSource pension plan's lump sum payouts for 2013 would exceed the plan's 2013 service cost plus interest cost and, therefore, settlement accounting was required. A settlement charge of $20.7 million was recorded during the first quarter of 2013. As a result of the settlement, the pension plan was remeasured as of February 28, 2013 resulting in a decrease to the pension benefit obligation, net of plan assets, of $18.6 million, and net decreases to regulatory assets and accumulated other comprehensive loss of $36.1 million and $3.2 million, respectively. During the second quarter of 2013, NiSource continued to apply settlement accounting for the pension plan and recognized an additional settlement charge of $3.6 million. As a result of the additional settlement, the pension plan was remeasured as of May 31, 2013 resulting in a decrease to the pension benefit obligation, net of plan assets, of $30.7 million, and net decreases to regulatory assets and accumulated other comprehensive loss of $30.8 million and $3.5 million, respectively. During the third quarter of 2013, NiSource continued to apply settlement accounting for the pension plan and recognized an additional settlement charge of $4.0 million. As a result of the additional settlement, the pension plan was remeasured as of August 31, 2013 resulting in a decrease to the pension benefit obligation, net of plan assets, of $1.7 million, a net decrease to regulatory assets of $6.5 million and a net increase to accumulated other comprehensive loss $0.8 million. Net periodic pension benefit cost for 2013 was decreased by $3.6 million as a result of the remeasurements.
	The following table provides the key assumptions that were used to calculate the pension benefit obligation and the net periodic benefit cost at the measurement dates of August 31, 2013, May 31, 2013, February 28, 2013 and December 31, 2012:
		31-Aug-13			31-May-13			28-Feb-13			31-Dec-12
	Actuarial Assumptions
	Discount Rate	4.25	%		3.75	%		3.5	%		3.63	%
	Expected return on assets	8.3	%		8.3	%		8.3	%		8.3	%

Variable_Interests_and_Variabl

Variable Interests and Variable Interest Entities	9 Months Ended
	Sep. 30, 2013
Variable Interest Entities And Equity Investments [Abstract]	'
Variable Interest Entities And Equity Investments	'
	Variable Interests and Variable Interest Entities
	In general, a VIE is an entity that (1) has an insufficient amount of at-risk equity to permit the entity to finance its activities without additional financial subordinated support provided by any parties, (2) whose at-risk equity owners, as a group, do not have power, through voting rights or similar rights, to direct activities of the entity that most significantly impact the entity’s economic performance or (3) whose at-risk owners do not absorb the entity’s losses or receive the entity’s residual return. A VIE is required to be consolidated by a company if that company is determined to be the primary beneficiary of the VIE.
	NiSource consolidates those VIEs for which it is the primary beneficiary. NiSource considers quantitative and qualitative elements in determining the primary beneficiary. Qualitative measures include the ability to control an entity and the obligation to absorb losses or the right to receive benefits.
	NiSource’s analysis includes an assessment of guarantees, operating leases, purchase agreements, and other contracts, as well as its investments and joint ventures. For items that have been identified as variable interests, or where there is involvement with an identified VIE, an in-depth review of the relationship between the relevant entities and NiSource is made to evaluate qualitative and quantitative factors to determine the primary beneficiary, if any, and whether additional disclosures would be required under the current standard.
	Northern Indiana has a service agreement with Pure Air, a general partnership between Air Products and Chemicals, Inc. and First Air Partners LP, under which Pure Air provides scrubber services to reduce sulfur dioxide emissions for Units 7 and 8 at the Bailly Generating Station. NiSource has made an exhaustive effort to obtain information needed from Pure Air to determine the status of Pure Air as a VIE. However, Northern Indiana has not been able to obtain this information and as a result, it is unclear whether Pure Air is a VIE and if Northern Indiana is the primary beneficiary. Northern Indiana will continue to request the information required to determine whether Pure Air is a VIE. Northern Indiana has no exposure to loss related to the service agreement with Pure Air and payments under this agreement were $17.1 million and $16.5 million for the nine months ended September 30, 2013 and 2012, respectively.

LongTerm_Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2013
Long-term Debt, Current and Noncurrent [Abstract]	'
Long-Term Debt	'
	Long-Term Debt
	On October 10, 2013, NiSource Finance issued $500.0 million of 5.65% senior unsecured notes that mature on February 1, 2045.
	On August 19, 2013, Northern Indiana redeemed $30.0 million of 7.16% medium term notes.
	On July 22, 2013, Northern Indiana redeemed $5.0 million of 7.21% medium term notes.
	On July 8, 2013, Northern Indiana redeemed $15.0 million of 7.35% medium term notes.
	On June 3, 2013, Northern Indiana redeemed $18.0 million of 5.20% pollution control bonds.
	On April 12, 2013, NiSource Finance issued $750.0 million of 4.80% senior unsecured notes that mature on February 15, 2044.
	On March 1, 2013, NiSource Finance redeemed $420.3 million of 6.15% senior unsecured notes.
	On April 5, 2012, NiSource Finance negotiated a $250.0 million three-year bank term loan with a syndicate of banks having an original maturity date of April 3, 2015. On April 15, 2013, NiSource Finance amended the term loan to add an additional lender to the syndicate of banks, increase borrowings under the term loan to $325.0 million and extend the maturity date to April 15, 2016. Borrowings under the term loan have an interest rate of LIBOR plus 125 basis points.

ShortTerm_Borrowings

Short-Term Borrowings	9 Months Ended
	Sep. 30, 2013
Short-term Debt [Abstract]	'
Short-Term Borrowings	'
	Short-Term Borrowings
	On September 30, 2013, NiSource Finance amended its existing revolving credit facility with a syndicate of banks led by Barclays Capital to expand capacity to $2.0 billion and extend the termination date to September 28, 2018. The purpose of the facility is to fund ongoing working capital requirements including the provision of liquidity support for NiSource’s $1.5 billion commercial paper program, provide for issuance of letters of credit, and also for general corporate purposes. At September 30, 2013, NiSource had no outstanding borrowings under this facility.
	During June 2011, NiSource Finance implemented a new commercial paper program with a program limit of up to $500.0 million with a dealer group comprised of Barclays, Citigroup, Credit Suisse and Wells Fargo. The program capacity was expanded to $1.5 billion with the addition of RBS as a fifth dealer on February 15, 2013. Commercial paper issuances are supported by available capacity under NiSource’s $2.0 billion unsecured revolving credit facility. At September 30, 2013, NiSource had $612.5 million of commercial paper outstanding.
	As of September 30, 2013 and December 31, 2012, NiSource had $39.2 million and $36.4 million of stand-by letters of credit outstanding, of which $21.3 million and $18.3 million were under the revolving credit facility, respectively.
	Transfers of accounts receivable are accounted for as secured borrowings resulting in the recognition of short-term debt on the Condensed Consolidated Balance Sheets (unaudited) in the amount of $208.3 million and $233.3 million as of September 30, 2013 and December 31, 2012, respectively. Refer to Note 9, “Transfers of Financial Assets,” for additional information.
	(in millions)	September 30,		December 31,
		2013		2012
	Commercial Paper weighted average interest rate of 0.67% and 1.11% at September 30, 2013 and December 31, 2012, respectively.	$	612.5	$	499.6
	Credit facilities borrowings weighted average interest rate of 3.73% at December 31, 2012.	—		44
	Accounts receivable securitization facility borrowings	208.3		233.3
	Total short-term borrowings	$	820.8	$	776.9
	Given their turnover is less than 90 days, cash flows related to the borrowings and repayments of the items listed above are presented net in the Condensed Statements of Consolidated Cash Flows (unaudited).

ShareBased_Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2013
Share-based Compensation [Abstract]	'
Share-Based Compensation	'
	Share-Based Compensation
	The stockholders approved and adopted the NiSource Inc. 2010 Omnibus Incentive Plan (the “Omnibus Plan”), at the Annual Meeting of Stockholders held on May 11, 2010. The Omnibus Plan provides for awards to employees and non-employee directors of incentive and nonqualified stock options, stock appreciation rights, restricted stock and restricted stock units, performance shares, performance units, cash-based awards and other stock-based awards. The Omnibus Plan provides that the number of shares of common stock of NiSource available for awards is 8,000,000 plus the number of shares subject to outstanding awards granted under either the 1994 Plan or the Director Plan (described below) that expire or terminate for any reason. No further awards are permitted to be granted under the 1994 Plan or the Director Plan. At September 30, 2013, there were 6,734,008 shares reserved for future awards under the Omnibus Plan.
	Prior to May 11, 2010, NiSource issued long-term equity incentive grants to key management employees under a long-term incentive plan approved by stockholders on April 13, 1994 (“1994 Plan”). The types of equity awards previously authorized under the 1994 Plan did not significantly differ from those permitted under the Omnibus Plan.
	NiSource recognized stock-based employee compensation expense of $8.8 million and $6.3 million for the three months ended September 30, 2013, and 2012, respectively, as well as related tax benefits of $3.2 million and $2.2 million, respectively. For the nine months ended September 30, 2013, and 2012, stock-based employee compensation expense of $17.5 million and $13.6 million was recognized, respectively, as well as related tax benefits of $6.1 million and $5.0 million, respectively.
	As of September 30, 2013, the total remaining unrecognized compensation cost related to nonvested awards amounted to $21.8 million, which will be amortized over the weighted-average remaining requisite service period of 2.0 years.
	Stock Options. As of September 30, 2013, approximately 0.5 million options were outstanding and exercisable with a weighted average strike price of $22.44. No options were granted during the nine months ended September 30, 2013 and 2012. As of September 30, 2013, the aggregate intrinsic value for the options outstanding and exercisable was $4.5 million. During the nine months ended September 30, 2013 and 2012, cash received from the exercise of options was $22.6 million and $24.7 million, respectively.
	Restricted Stock Units and Restricted Stock. During the nine months ended September 30, 2013, NiSource granted 69,651 restricted stock units and shares of restricted stock, subject to service conditions. The total grant date fair value of restricted stock units and shares of restricted stock was $1.8 million, based on the average market price of NiSource’s common stock at the date of each grant less the present value of any dividends not received during the vesting period, which will be expensed, net of forfeitures, over the vesting period which is generally three years. If the employee terminates employment before the service conditions lapse due to (1) Retirement or Disability (as defined in the award agreement), or (2) death, the employment conditions will lapse with respect to a pro rata portion of the shares of restricted stock and restricted stock units on the date of termination. In the event of a Change-in-Control (as defined in the award agreement), all unvested shares of restricted stock and restricted stock units will immediately vest. Termination due to any other reason will result in all unvested shares of restricted stock and restricted stock units awarded being forfeited effective on the employee’s date of termination. As of September 30, 2013, 371,870 nonvested (all of which are expected to vest) restricted stock units and shares of restricted stock were granted and outstanding.
	Performance Shares. During the nine months ended September 30, 2013, NiSource granted 664,776 performance shares subject to performance conditions. The grant date fair value of the awards was $15.7 million, based on the average market price of NiSource’s common stock at the date of each grant less the present value of dividends not received during the vesting period which will be expensed, net of forfeitures, over the three year requisite service period. The performance conditions are based on achievement of certain non-GAAP financial measures: cumulative net operating earnings, that NiSource defines as income from continuing operations adjusted for certain items; and cumulative funds from operations that NiSource defines as net operating cash flows provided by continuing operations; and relative total shareholder return, a non-GAAP market measure that NiSource defines as the annualized growth in the dividends and share price of a share of NiSource’s common stock (calculated using a 20 trading day average of NiSource’s closing price beginning December 31, 2012 and ending on December 31, 2015) compared to the total shareholder return performance of a predetermined peer group of companies. The service conditions lapse on February 29, 2016 when the shares vest provided the performance criteria are satisfied. In general, if the employee terminates employment before February 29, 2016 due to (1) Retirement or Disability (as defined in the award agreement), or (2) death, the employment conditions will lapse with respect to a pro rata portion of the performance shares payable at target on the date of termination provided the performance criteria are met. In the event of a Change-in-Control (as defined in the award agreement), all unvested performance shares will immediately vest. Termination due to any other reason will result in all performance shares awarded being forfeited effective on the employee’s date of termination. As of September 30, 2013, 1,974,337 nonvested performance shares were granted and outstanding.
	Non-employee Director Awards. As of May 11, 2010, awards to non-employee directors may be made only under the Omnibus Plan. Currently, restricted stock units are granted annually to non-employee directors, subject to a non-employee director’s election to defer receipt of such restricted stock unit award. The non-employee director’s restricted stock units vest on the last day of the non-employee director’s annual term corresponding to the year the restricted stock units were awarded subject to special pro-rata vesting rules in the event of Retirement or Disability (as defined in the award agreement), or death. The vested restricted stock units are payable as soon as practicable following vesting except as otherwise provided pursuant to the non-employee director’s election to defer. As of September 30, 2013, 148,702 restricted stock units are outstanding to non-employee directors under the Omnibus Plan.
	Only restricted stock units remain outstanding under the prior plan for non-employee directors, the Amended and Restated Non-employee Director Stock Incentive Plan (the “Director Plan”). All such awards are fully vested and shall be distributed to the directors upon their separation from the Board. As of September 30, 2013, 181,106 restricted stock units remain outstanding under the Director Plan and as noted above no further shares may be awarded under the Director Plan.
	401(k) Match, Profit Sharing and Company Contribution. NiSource has a voluntary 401(k) savings plan covering eligible employees that allows for periodic discretionary matches as a percentage of each participant’s contributions in newly issued shares of common stock. NiSource also has a retirement savings plan that provides for discretionary profit sharing contributions of shares of common stock to eligible employees based on earnings results; and eligible exempt employees hired after January 1, 2010, receive a non-elective company contribution of three percent of eligible pay in shares of common stock. For the quarters ended September 30, 2013 and 2012, NiSource recognized 401(k) match, profit sharing and non-elective contribution expense of $7.9 million and $6.7 million, respectively. For the nine months ended September 30, 2013 and 2012, NiSource recognized 401(k) match, profit sharing and non-elective contribution expense of $22.2 million and $19.4 million, respectively.

Other_Commitments_And_Continge

Other Commitments And Contingencies	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Other Commitments And Contingencies	'
	Other Commitments and Contingencies
	A.    Guarantees and Indemnities. As a part of normal business, NiSource and certain subsidiaries enter into various agreements providing financial or performance assurance to third parties on behalf of certain subsidiaries. Such agreements include guarantees and stand-by letters of credit. These agreements are entered into primarily to support or enhance the creditworthiness otherwise attributed to a subsidiary on a stand-alone basis, thereby facilitating the extension of sufficient credit to accomplish the subsidiaries’ intended commercial purposes. The total guarantees and indemnities in existence at September 30, 2013 and the years in which they expire were:
	(in millions)	Total		2013		2014		2015		2016		2017		After
	Guarantees of subsidiaries debt	$	7,210.50	$	—	$	500	$	230	$	616.5	$	507	$	5,357.00
	Guarantees supporting commodity transactions of subsidiaries	10.7		10.7		—		—		—		—		—
	Accounts receivable securitization	208.3		208.3		—		—		—		—		—
	Lines of credit	612.5		612.5		—		—		—		—		—
	Letters of credit	39.2		0.7		22.3		16.2		—		—		—
	Other guarantees	132.3		18.1		48.4		3		—		—		62.8
	Total commercial commitments	$	8,213.50	$	850.3	$	570.7	$	249.2	$	616.5	$	507	$	5,419.80
	Guarantees of Subsidiaries Debt. NiSource has guaranteed the payment of $7.2 billion of debt for various wholly-owned subsidiaries including NiSource Finance and Columbia of Massachusetts, and through a support agreement, Capital Markets, which is reflected on NiSource’s Condensed Consolidated Balance Sheets (unaudited). The subsidiaries are required to comply with certain covenants under the debt indenture and in the event of default, NiSource would be obligated to pay the debt’s principal and related interest. NiSource does not anticipate its subsidiaries will have any difficulty maintaining compliance. On October 3, 2011, NiSource executed a Second Supplemental Indenture to the original Columbia of Massachusetts Indenture dated April 1, 1991, for the specific purpose of guaranteeing Columbia of Massachusetts’ outstanding medium-term notes.
	Guarantees Supporting Commodity Transactions of Subsidiaries. NiSource has issued guarantees, which support up to $10.7 million of commodity-related payments for its current subsidiaries involved in energy marketing activities. These guarantees were provided to counterparties in order to facilitate physical and financial transactions involving natural gas services. To the extent liabilities exist under the commodity-related contracts subject to these guarantees, such liabilities are included in the Condensed Consolidated Balance Sheets (unaudited).
	Lines and Letters of Credit and Accounts Receivable Advances. On September 30, 2013, NiSource Finance amended its existing revolving credit facility with a syndicate of banks led by Barclays Capital to expand capacity to $2.0 billion and extend the termination date to September 28, 2018. The purpose of the facility is to fund ongoing working capital requirements including the provision of liquidity support for NiSource’s $1.5 billion commercial paper program, provide for the issuance of letters of credit, and also for general corporate purposes. At September 30, 2013, NiSource had no borrowings under its five-year revolving credit facility, $612.5 million in commercial paper outstanding and $208.3 million outstanding under its accounts receivable securitization agreements. At September 30, 2013, NiSource issued stand-by letters of credit of approximately $39.2 million for the benefit of third parties. See Note 15, “Short-Term Borrowings,” for additional information.
	Other Guarantees or Obligations. NiSource has additional purchase and sales agreement guarantees totaling $28.0 million, which guarantee performance of the seller’s covenants, agreements, obligations, liabilities, representations and warranties under the agreements. No amounts related to the purchase and sales agreement guarantees are reflected in the Condensed Consolidated Balance Sheets (unaudited). Management believes that the likelihood NiSource would be required to perform or otherwise incur any significant losses associated with any of the aforementioned guarantees is remote.
	NiSource has on deposit a letter of credit with Union Bank, N.A., Collateral Agent, in a debt service reserve account in association with Millennium's notes as required under the Deposit and Disbursement Agreement that governs the Millennium notes. This account is to be drawn upon by the note holders in the event that Millennium is delinquent on its principal and interest payments. The value of NiSource’s letter of credit represents 47.5% (NiSource’s ownership percentage in Millennium) of the Debt Service Reserve Account requirement, or $16.2 million. The total exposure for NiSource is $16.2 million. NiSource has an accrued liability of $1.5 million related to the inception date fair value of this guarantee as of September 30, 2013.
	NiSource has issued other guarantees supporting derivative related payments associated with interest rate swap agreements issued by NiSource Finance, operating leases for many of its subsidiaries and for other agreements entered into by its current and former subsidiaries.
	B.    Other Legal Proceedings. In the normal course of its business, NiSource and its subsidiaries have been named as defendants in various legal proceedings. In the opinion of management, the ultimate disposition of these currently asserted claims will not have a material impact on NiSource’s consolidated financial statements.
	In 2003, the Company divested itself of a certain non-utility subsidiary, which subsequently became involved in litigation around business transactions, some of which predated its sale to a third party. Successors in interest to that third party looked to the Company for indemnification under the Asset Purchase Agreement (“APA") negotiated by the Company at the time of sale. As the litigation wound down and was concluded over the years, the Company advanced settlement and defense costs associated with all claims made in the litigation and reserved its rights to seek reimbursement for claims potentially not within the scope of the indemnities under the APA. Later, the Company looked to the successors in interest to the APA for reimbursement of settlement and defense related charges associated with claims that were not subject to the indemnification provisions in the APA. Ultimately, the amount of claims subject to the indemnities provided for in the APA was the subject of an arbitration claim between the Company and the successors in interest to the APA. In January of 2013, the parties to the arbitration proceeding agreed that the Company would be reimbursed $17.5 million for settlement amounts advanced and defense costs incurred beyond the scope of indemnities under the APA, which has since been paid to the Company in full. This amount was recorded in income from discontinued operations, net of tax, in the first quarter of 2013.
	C.    Environmental Matters. NiSource operations are subject to environmental statutes and regulations related to air quality, water quality, hazardous waste and solid waste. NiSource believes that it is in substantial compliance with those environmental regulations currently applicable to its operations and believes that it has all necessary permits to conduct its operations.
	It is management’s continued intent to address environmental issues in cooperation with regulatory authorities in such a manner as to achieve mutually acceptable compliance plans. However, there can be no assurance that fines and penalties will not be incurred. Management expects a significant portion of environmental assessment and remediation costs to be recoverable through rates for certain NiSource companies.
	As of September 30, 2013 and December 31, 2012, NiSource had recorded reserves of approximately $149.5 million and $160.6 million, respectively, to cover environmental remediation at various sites. The current portion of this reserve is included in "Legal and environmental reserves" in the Condensed Consolidated Balance Sheets (unaudited). The noncurrent portion is included in "Other noncurrent liabilities" in the Condensed Consolidated Balance Sheets (unaudited). NiSource accrues for costs associated with environmental remediation obligations when the incurrence of such costs is probable and the amounts can be reasonably estimated. The original estimates for cleanup can differ materially from the amount ultimately expended. The actual future expenditures depend on many factors, including currently enacted laws and regulations, the nature and extent of contamination, the method of cleanup, and the availability of cost recovery from customers. These expenditures are not currently estimable at some sites. NiSource periodically adjusts its reserves as information is collected and estimates become more refined.
	Air
	The actions listed below could require further reductions in emissions from various emission sources. NiSource will continue to closely monitor developments in these matters.
	Climate Change. Future legislative and regulatory programs could significantly restrict emissions of GHGs or could impose a cost or tax on GHG emissions. Recently, proposals have been developed to implement federal, state and regional GHG programs and to create renewable energy standards.
	In the first quarter of 2012, the EPA proposed an output-based carbon standard for new power plants. On September 20, 2013, the EPA announced withdrawal of the proposed standard and released a new proposal. The newly proposed standard would, for the first time, set national limits on the amount of carbon emissions allowed from new power plants. The revised numerical limit requires that compliance for new coal-fired plants include capture and sequestration of carbon dioxide. In addition, the EPA acknowledged that it intends to regulate existing sources with a proposed rule expected in 2014.
	If the EPA develops a GHG new source performance standard for existing units or if a federal or state comprehensive climate change bill were to be enacted into law, the impact on NiSource's financial performance would depend on a number of factors, including the overall level of required GHG reductions, the renewable energy targets, the degree to which offsets may be used for compliance, the amount of recovery allowed from customers, and the extent to which NiSource would be entitled to receive CO2 allowances at no cost. Comprehensive federal or state GHG regulation could result in additional expense or compliance costs that may not be fully recoverable from customers and could materially impact NiSource's financial results.
	National Ambient Air Quality Standards. The CAA requires the EPA to set national air quality standards for particulate matter and five other pollutants (the NAAQS) considered harmful to public health and the environment. Periodically the EPA imposes new or modifies existing NAAQS. States that contain areas that do not meet the new or revised standards must take steps to maintain or achieve compliance with the standards. These steps could include additional pollution controls on boilers, engines, turbines, and other facilities owned by electric generation, gas distribution, and gas transmission operations.
	The following NAAQS were recently added or modified:
	Particulate Matter: In December 2009, the EPA issued area designations for the 2006 24-hour PM2.5 standard, and several counties in which NiSource operates were designated as non-attainment. In addition, a final rule was promulgated in December 2012 that lowered the annual PM2.5 standard from 15 to 12 micrograms per cubic meter. NiSource will continue to monitor these matters and cannot estimate their impact at this time.
	Ozone (eight hour): On September 2, 2011, the EPA announced it would implement its 2008 eight-hour ozone NAAQS rather than tightening the standard in 2012. The EPA will review, and possibly revise, the standard in 2013 consistent with CAA requirements. In addition, the EPA has designated the Chicago metropolitan area, including the area in which Northern Indiana operates one of its electric generation facilities, as non-attainment for ozone. NiSource will continue to monitor this matter and cannot estimate the impact of any new rules at this time.
	Nitrogen Dioxide (NO2): The EPA revised the NO2 NAAQS by adding a one-hour standard while retaining the annual standard. The new standard could impact some NiSource combustion sources. The EPA designated all areas of the country as unclassifiable/attainment in January 2012. After the establishment of a new monitoring network and possible modeling implementation, areas will potentially be re-designated sometime in 2016. States with areas that do not meet the standard will be required to develop rules to bring areas into compliance within five years of designation. Additionally, under certain permitting circumstances emissions from some existing NiSource combustion sources may need to be assessed and mitigated. NiSource will continue to monitor this matter and cannot estimate the impact of these rules at this time.
	Waste
	NiSource subsidiaries are potentially responsible parties at waste disposal sites under the CERCLA (commonly known as Superfund) and similar state laws. Additionally, a program has been instituted to identify and investigate former MGP sites where Gas Distribution Operations subsidiaries or predecessors may have liability. The program has identified 67 such sites where liability is probable. Remedial actions at many of these sites are being overseen by state or federal environmental agencies through consent agreements or voluntary remediation agreements.
	NiSource utilizes a probabilistic model to estimate its future remediation costs related to its MGP sites. The model was prepared with the assistance of a third party and incorporates NiSource and general industry experience with remediating MGP sites. NiSource completes an annual refresh of the model in the second quarter of each fiscal year. No material changes to the liability were noted as a result of the refresh completed as of June 30, 2013. The total liability at NiSource related to the facilities subject to remediation was $131.4 million and $132.6 million at September 30, 2013 and December 31, 2012, respectively. The liability represents NiSource’s best estimate of the probable cost to remediate the facilities. NiSource believes that it is reasonably possible that remediation costs could vary by as much as $25 million in addition to the costs noted above. Remediation costs are estimated based on the best available information, applicable remediation standards at the balance sheet date, and experience with similar facilities.
	Additional Issues Related to Individual Business Segments
	The sections below describe various regulatory actions that affect Columbia Pipeline Group Operations, Electric Operations, and certain other discontinued operations for which NiSource has retained a liability.
	Columbia Pipeline Group Operations.
	Waste
	Columbia Transmission continues to conduct characterization and remediation activities at specific sites under a 1995 AOC (subsequently modified in 1996 and 2007). The 1995 AOC originally covered 245 major facilities, approximately 13,000 liquid removal points, approximately 2,200 mercury measurement stations and about 3,700 storage well locations. As a result of the 2007 amendment, approximately 50 facilities remain subject to the terms of the AOC. During the third quarter of 2011, Columbia Transmission completed a study to estimate its future remediation requirements related to the AOC. Columbia Transmission accordingly increased its liability for estimated remediation costs by $25.6 million. Since the third quarter of 2011, Columbia Transmission has been monitoring its liability on a quarterly basis and performed an annual refresh of the study during the second quarter of subsequent years, with no material changes recorded. The total liability at Columbia Transmission related to the facilities subject to remediation was $11.8 million and $21.7 million at September 30, 2013 and December 31, 2012, respectively. The liability represents Columbia Transmission’s best estimate of the cost to remediate the facilities or manage the sites. Remediation costs are estimated based on the information available, applicable remediation standards, and experience with similar facilities. Columbia Transmission expects that the remediation for these facilities will be substantially completed in 2015.
	One of the facilities subject to the 1995 AOC is the Majorsville Operations Center, which was remediated under an EPA approved Remedial Action Work Plan in summer 2008. The completed work was approved by EPA, and Columbia Transmission continues to monitor the site subject to EPA oversight. On April 23, 2009, the PADEP issued Columbia Transmission an NOV, alleging that the remediation did not fully address the site's impact on an adjacent stream, which Columbia Transmission disputes. The NOV asserts violations of the Pennsylvania Clean Streams Law and the Pennsylvania Solid Waste Management Act and includes a settlement demand in the amount of $1 million. The PADEP has not initiated a legal proceeding since issuance of the NOV. Columbia Transmission believes that it is reasonably unlikely that a penalty will be assessed.
	Electric Operations.
	Air
	Northern Indiana expects to become subject to a number of new air-quality mandates in the next several years. These mandates may require Northern Indiana to make capital improvements to its electric generating stations. The cost of capital improvements is estimated to be $860 million, of which approximately $350 million remains to be spent. This figure includes additional capital improvements associated with the New Source Review Consent Decree and the Utility Mercury and Air Toxics Standards Rule. Northern Indiana believes that the capital costs will likely be recoverable from ratepayers.
	Sulfur dioxide: In June 2010, the EPA promulgated a revised primary one-hour SO2 NAAQS. The EPA completed its initial round of SO2 nonattainment designations in July 2013, based upon ambient air monitoring data. Counties containing Northern Indiana coal-fired generating stations were not designated as nonattainment, but they will be addressed in future action by the EPA. Northern Indiana will continue to monitor developments in these matters but does not anticipate a material impact.
	Cross-State Air Pollution Rule / Clean Air Interstate Rule (CAIR) / Transport Rule: On July 6, 2011, the EPA announced its replacement for the 2005 CAIR to reduce the interstate transport of fine particulate matter and ozone. The CSAPR reduces overall emissions of SO2 and NOx by setting state-wide caps on power plant emissions. The CSAPR limits emissions, including Northern Indiana's, and restricted emission allowance trading programs were scheduled to begin in 2012. In a decision issued on August 21, 2012 the D.C. Circuit Court vacated the CSAPR leaving the CAIR trading program provisions and requirements in place. The EPA subsequently petitioned for a writ of certiorari, and the Supreme Court granted this writ on June 24, 2013. Oral arguments are scheduled for December 10, 2013 and a decision is expected sometime next year. These legal developments do not significantly impact Northern Indiana's current emissions control plans. Northern Indiana utilizes the inventory model in accounting for emission allowances issued under the CAIR program whereby these allowances were recognized at zero cost upon receipt from the EPA. Northern Indiana believes its current multi-pollutant compliance plan and New Source Review Consent Decree capital investments will allow Northern Indiana to meet the emission requirements of CAIR, while a replacement for CSAPR is developed to address the court's decision.
	Utility Mercury and Air Toxics Standards Rule:   On February 8, 2008, the United States Court of Appeals for the District of Columbia Circuit vacated two EPA rules that are the basis for the Indiana Air Pollution Control Board’s Clean Air Mercury Rule (CAMR) that established utility mercury emission limits in two phases (2010 and 2018) and a cap-and-trade program to meet those limits. In response to the vacatur, the EPA pursued a new Section 112 rulemaking to establish MACT standards for electric utilities. The EPA finalized the MATS rule on December 16, 2011. Compliance for Northern Indiana’s affected units is required by April 2016. Northern Indiana has developed a plan for further environmental controls to comply with MATS.
	New Source Review:   On September 29, 2004, the EPA issued an NOV to Northern Indiana for alleged violations of the CAA and the Indiana SIP. The NOV alleged that modifications were made to certain boiler units at three of Northern Indiana’s generating stations between the years 1985 and 1995 without obtaining appropriate air permits for the modifications. Northern Indiana, the EPA, the Department of Justice, and IDEM have settled the matter through a consent decree, entered on July 22, 2011.
	Water
	The Phase II Rule of the Clean Water Act Section 316(b), which requires all large existing steam electric generating stations to meet certain performance standards to reduce the effects on aquatic organisms at their cooling water intake structures, became effective on September 7, 2004. Under this rule, stations will either have to demonstrate that the performance of their existing fish protection systems meet the new standards or develop new systems, such as a closed-cycle cooling tower. Various court challenges and EPA responses ensued. The EPA announced a proposed rule and is obligated to finalize a rule in 2013. Northern Indiana will continue to monitor this matter but cannot estimate the cost of compliance at this time.
	On June 7, 2013, the EPA published a proposed rule to amend the effluent limitations guidelines and standards for the Steam Electric Power Generating category. Northern Indiana anticipates the rule to be finalized in 2014 and will continue to monitor this matter but cannot estimate the cost of compliance at this time.
	Waste
	On March 31, 2005, the EPA and Northern Indiana entered into an AOC under the authority of Section 3008(h) of the RCRA for the Bailly Station. The order requires Northern Indiana to identify the nature and extent of releases of hazardous waste and hazardous constituents from the facility. Northern Indiana must also remediate any release of hazardous constituents that present an unacceptable risk to human health or the environment. In July 2012, the EPA issued a Final Decision for Areas A and B of the Bailly facility. Remedial activities in those areas have commenced and may continue into 2014. The process to investigate and select appropriate remedial activities at a third area is ongoing.
	The Indiana Department of Environmental Management requested that Northern Indiana enter into AOCs to identify the nature and extent of releases of hazardous waste and hazardous constituents at the Michigan City and Mitchell Generating Stations. The final AOC for the Michigan City Generating Station became effective in October 2013, and investigation activities are expected to commence in 2014. A final AOC for the Mitchell Generating Station is expected to be effective in 2014. Northern Indiana cannot estimate the cost of compliance with any AOCs at this time.
	On June 21, 2010, the EPA published a proposed rule for regulation of CCRs. The proposal outlines multiple regulatory approaches that the EPA is considering. These proposed regulations could negatively affect Northern Indiana’s ongoing byproduct reuse programs and would impose additional requirements on its management of coal combustion residuals. Northern Indiana will continue to monitor developments in this matter and cannot estimate the cost of compliance at this time.
	Other Operations.
	Waste
	NiSource affiliates have retained environmental liabilities, including cleanup liabilities associated with some of its former operations. Four sites are associated with its former propane operations and ten sites associated with former petroleum operations. At one of those sites, an AOC has been signed with the EPA to address petroleum residue in soil and groundwater.
	D.     Other Matters. On November 23, 2012, while Columbia of Massachusetts was investigating the source of an odor of gas at a service location in Springfield, Massachusetts, a gas service line was pierced and an explosion occurred. While this explosion impacted multiple buildings and resulted in several injuries, no life threatening injuries or fatalities have been reported. Columbia of Massachusetts is fully cooperating with both the Massachusetts DPU and the Occupational Safety & Health Administration in their investigations of this incident. Columbia of Massachusetts believes any costs associated with damages, injuries, and other losses related to this incident are substantially covered by insurance. Any amounts not covered by insurance are not expected to have a material impact on NiSource's consolidated financial statements. In accordance with GAAP, NiSource recorded any reserves and the related insurance recoveries resulting from this incident on a gross basis within the Condensed Consolidated Balance Sheets (unaudited).

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Loss	9 Months Ended
	Sep. 30, 2013
Other Comprehensive Income (Loss), Tax [Abstract]	'
Accumulated Other Comprehensive Loss	'
	Accumulated Other Comprehensive Loss
	The following tables display the components of Accumulated Other Comprehensive Loss for the three and nine months ended September 30, 2013:
	Three Months Ended September 30, 2013 (in millions)	Gains and Losses on Securities(1)			Gains and Losses on Cash Flow Hedges(1)			Pension and OPEB Items(1)			Accumulated
											Other
											Comprehensive
											Loss(1)
	Balance as of July 1, 2013	$	(0.7	)	$	(27.2	)	$	(34.1	)	$	(62.0	)
	Other comprehensive income before reclassifications	1			(0.1		)	(0.6		)	0.3
	Amounts reclassified from accumulated other comprehensive income	(0.1		)	0.7			0.7			1.3
	Net current-period other comprehensive income	0.9			0.6			0.1			1.6
	Balance as of September 30, 2013	$	0.2		$	(26.6	)	$	(34.0	)	$	(60.4	)
	Nine Months Ended September 30, 2013 (in millions)	Gains and Losses on Securities(1)			Gains and Losses on Cash Flow Hedges(1)			Pension and OPEB Items(1)			Accumulated
											Other
											Comprehensive
											Loss(1)
	Balance as of January 1, 2013	$	2.6		$	(28.6	)	$	(39.5	)	$	(65.5	)
	Other comprehensive income before reclassifications	(1.9		)	(0.1		)	2.6			0.6
	Amounts reclassified from accumulated other comprehensive income	(0.5		)	2.1			2.9			4.5
	Net current-period other comprehensive (loss) income	(2.4		)	2			5.5			5.1
	Balance as of September 30, 2013	$	0.2		$	(26.6	)	$	(34.0	)	$	(60.4	)
	(1)All amounts are net of tax. Amounts in parentheses indicate debits.
	Equity Investment
	As Millennium is an equity method investment, NiSource is required to recognize a proportional share of Millennium’s OCI. The remaining unrecognized loss at September 30, 2013 of $17.9 million, net of tax, related to terminated interest rate swaps is being amortized over the period ending June 2025 into earnings using the effective interest method through interest expense as interest payments are made by Millennium. The unrecognized loss of $17.9 million and $18.7 million at September 30, 2013 and December 31, 2012, respectively, is included in gains and losses on cash flow hedges above.

Business_Segment_Information

Business Segment Information	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Segments Of Business	'
	Business Segment Information
	Operating segments are components of an enterprise for which separate financial information is available and evaluated regularly by the chief operating decision maker in deciding how to allocate resources and assess performance. NiSource's Chief Executive Officer is the chief operating decision maker.
	At September 30, 2013, NiSource’s operations are divided into three primary business segments. The Gas Distribution Operations segment provides natural gas service and transportation for residential, commercial and industrial customers in Ohio, Pennsylvania, Virginia, Kentucky, Maryland, Indiana and Massachusetts. The Columbia Pipeline Group (formerly known as Gas Transmission and Storage) Operations segment offers gas transportation and storage services for LDCs, marketers and industrial and commercial customers located in northeastern, mid-Atlantic, midwestern and southern states along with unregulated businesses that include midstream services and development of mineral rights positions. The Electric Operations segment provides electric service in 20 counties in the northern part of Indiana.
	The following table provides information about business segments. NiSource uses operating income as its primary measurement for each of the reported segments and makes decisions on finance, dividends and taxes at the corporate level on a consolidated basis. Segment revenues include intersegment sales to affiliated subsidiaries, which are eliminated in consolidation. Affiliated sales are recognized on the basis of prevailing market, regulated prices or at levels provided for under contractual agreements. Operating income is derived from revenues and expenses directly associated with each segment.
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
	(in millions)	2013			2012			2013			2012
	REVENUES
	Gas Distribution Operations
	Unaffiliated	$	409.5		$	378.9		$	2,126.80		$	1,882.80
	Intersegment	—			0.1			0.2			0.4
	Total	409.5			379			2,127.00			1,883.20
	Columbia Pipeline Group Operations
	Unaffiliated	251.3			156.6			752			599.1
	Intersegment	31.4			31.5			105.9			105.4
	Total	282.7			188.1			857.9			704.5
	Electric Operations
	Unaffiliated	413.6			418.3			1,175.90			1,148.40
	Intersegment	0.1			0.2			0.5			0.6
	Total	413.7			418.5			1,176.40			1,149.00
	Corporate and Other
	Unaffiliated	2.4			2.4			5.8			7
	Intersegment	119.6			119.3			351.3			345.3
	Total	122			121.7			357.1			352.3
	Eliminations	(151.1		)	(151.1		)	(457.9		)	(451.7		)
	Consolidated Gross Revenues	$	1,076.80		$	956.2		$	4,060.50		$	3,637.30
	Operating Income (Loss)
	Gas Distribution Operations	$	(5.0	)	$	10.4		$	279.1		$	263.4
	Columbia Pipeline Group Operations	98.7			38.8			321			268.9
	Electric Operations	87.5			83.7			212.2			200.2
	Corporate and Other	(4.8		)	(1.4		)	(13.0		)	1
	Consolidated Operating Income	$	176.4		$	131.5		$	799.3		$	733.5

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2013
Supplemental Cash Flow Information [Abstract]	'
Supplemental Cash Flow Information	'
	Supplemental Cash Flow Information
	The following table provides additional information regarding NiSource’s Condensed Statements of Consolidated Cash Flows (unaudited) for the nine months ended September 30, 2013 and 2012:
		Nine Months Ended
		September 30,
	(in millions)	2013		2012
	Supplemental Disclosures of Cash Flow Information
	Non-cash transactions:
	Capital expenditures included in current liabilities	$	202.7	$	119.6
	Stock issuance to employee savings plans	22.2		19.4
	Schedule of interest and income taxes paid:
	Cash paid for interest, net of interest capitalized amounts	$	359.4	$	336.1
	Cash paid for income taxes	8.5		8.4

Risk_Management_Activities_Pol

Risk Management Activities (Policy)	9 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Derivatives, Policy	'
	Accounting Policy for Derivative Instruments.    The ASC topic on accounting for derivatives and hedging requires an entity to recognize all derivatives as either assets or liabilities on the Condensed Consolidated Balance Sheets (unaudited) at fair value, unless such contracts are exempted, such as normal purchase and normal sale contracts under the provisions of the ASC topic. The accounting for changes in the fair value of a derivative depends on the intended use of the derivative and resulting designation.
	NiSource uses a variety of derivative instruments (exchange traded futures and options, physical forwards and options, commodity swaps, and interest rate swaps) to effectively manage its commodity price risk and interest rate risk exposure. If certain conditions are met, a derivative may be specifically designated as (a) a hedge of the exposure to changes in the fair value of a recognized asset or liability or an unrecognized firm commitment, or (b) a hedge of the exposure to variable cash flows of a forecasted transaction. In order for a derivative contract to be designated as a hedge, the relationship between the hedging instrument and the hedged item or transaction must be highly effective. The effectiveness test is performed at the inception of the hedge and each reporting period thereafter, throughout the period that the hedge is designated. Any amounts determined to be ineffective are recognized currently in earnings. For derivative contracts that qualify for the normal purchase and normal sales exception, a contract’s fair value is not recognized in the Condensed Consolidated Financial Statements (unaudited) until the contract is settled.
	Unrealized and realized gains and losses are recognized each period as components of AOCI, regulatory assets and liabilities or earnings depending on the designation of the derivative instrument and regulatory accounting treatment. For subsidiaries that utilize derivatives for cash flow hedges, the effective portions of the gains and losses are recorded to AOCI and are recognized in earnings concurrent with the disposition of the hedged risks. If a forecasted transaction corresponding to a cash flow hedge is no longer probable to occur, the accumulated gains or losses on the derivative are recognized currently in earnings. For fair value hedges, the gains and losses are recorded in earnings each period together with the change in the fair value of the hedged item. As a result of the rate-making process, the rate-regulated subsidiaries generally record gains and losses as regulatory liabilities or assets and recognize such gains or losses in earnings when both the contracts settle and the physical commodity flows. These gains and losses recognized in earnings are then subsequently recovered or passed back to customers in revenues through rates. When gains and losses are recognized in earnings, they are recognized in revenues or cost of sales for derivatives that correspond to commodity risk activities and are recognized in interest expense for derivatives that correspond to interest-rate risk activities.
	For its commodity price risk programs, NiSource has elected not to net the fair value amounts of its derivative instruments or the fair value amounts recognized for its right to receive or obligation to pay cash collateral arising from those derivative instruments recognized at fair value, which are executed with the same counterparty under a master netting arrangement. NiSource discloses amounts recognized for the right to reclaim cash collateral within “Restricted cash” and amounts recognized for the obligation to return cash collateral within “Other accruals” on the Condensed Consolidated Balance Sheets (unaudited).

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2013
Earnings Per Share [Abstract]	'
Computation Of Diluted Average Common Shares	'
		Three Months Ended		Nine Months Ended
		September 30,		September 30,
	(in thousands)	2013	2012	2013	2012
	Denominator
	Basic average common shares outstanding	312,842	290,328	312,053	285,891
	Dilutive potential common shares:
	Stock options	112	197	102	159
	Shares contingently issuable under employee stock plans	369	434	327	393
	Shares restricted under stock plans	490	654	477	626
	Forward agreements	—	8,399	—	9,609
	Diluted Average Common Shares	313,813	300,012	312,959	296,678

Discontinued_Operations_And_As1

Discontinued Operations And Assets And Liabilities Held For Sale (Tables)	9 Months Ended
	Sep. 30, 2013
Discontinued Operations And Assets And Liabilities Held For Sale [Abstract]	'
Assets And Liabilities Of Discontinued Operations And Held For Sale	'
	The assets and liabilities of discontinued operations and held for sale on the Consolidated Balance Sheet at December 31, 2012 by segment were:
	(in millions)
	Assets of discontinued operations and held for sale:	Property, plant and			Price risk management assets			Other Assets			Total
		equipment, net
	Gas Distribution Operations	$	21.5		$	—		$	4.5		$	26
	Electric Operations	—			—			0.7			0.7
	Corporate and Other	—			107			0.2			107.2
	Total	$	21.5		$	107		$	5.4		$	133.9
	Liabilities of discontinued operations and held for sale:				Price risk management liabilities			Other Liabilities			Total
	Gas Distribution Operations				$	—		$	3.3		$	3.3
	Electric Operations				—			0.6			0.6
	Corporate and Other				104.7			—			104.7
	Total				$	104.7		$	3.9		$	108.6
	Total assets and liabilities of discontinued operations and held for sale in the table above relate to the commercial and industrial portfolio of NiSource's unregulated natural gas marketing business and the service plan and leasing business lines of NiSource's Retail Services business.
	Results from discontinued operations are provided in the following table. These results are primarily from NiSource's Retail Services business, a settlement at NiSource's former exploration and production subsidiary, CER, NiSource's unregulated natural gas marketing business and Columbia Propane. For additional information regarding the settlement refer to Note 17-B, “Other Legal Proceedings,” in the Notes to Condensed Consolidated Financial Statements (unaudited).
		Three Months Ended								Nine Months Ended
		September 30,								September 30,
	(in millions)	2013				2012				2013			2012
	Revenues from Discontinued Operations	$	0.4			$	10.8			$	1.3		$	28.8
	Income from discontinued operations	0.1				4.5				12.2			8.6
	Income tax expense	—				1.8				4.7			3.2
	Income from Discontinued Operations - net of taxes	$	0.1			$	2.7			$	7.5		$	5.4
	(Loss) Gain on Disposition of Discontinued Operations - net of taxes	$	(1.5	)		$	—			$	34.9		$	—

Asset_Retirement_Obligations_T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2013
Asset Retirement Obligation [Abstract]	'
Changes In Company's Liability For Asset Retirement Obligations	'
	(in millions)	2013			2012
	Balance as of January 1,	$	160.4		$	146.4
	Accretion expense	0.9			0.8
	Accretion recorded as a regulatory asset/liability	6.5			6.6
	Additions	9.7			—
	Settlements	(1.3		)	(0.7		)
	Change in estimated cash flows	(0.7		)	(1.1		)
	Balance as of September 30,	$	175.5		$	152

Risk_Management_Activities_Tab

Risk Management Activities (Tables)	9 Months Ended
	Sep. 30, 2013
Derivative Instruments and Hedges, Assets [Abstract]	'
Commodity Price Risk Program Derivative Contracted Gross Volumes	'
		September 30, 2013			December 31, 2012
	Commodity Price Risk Program:
	Gas price volatility program derivatives (MMDth)	25.8			26.3
	Price Protection Service program derivatives (MMDth)	1			1.2
	DependaBill program derivatives (MMDth)	0.3			0.3
	Gas marketing program derivatives (MMDth)(1)(3)	—			9.1
	Gas marketing forward physical derivatives (MMDth)(2)(3)	—			8.4
	Electric energy program FTR derivatives (mw)	1,218.20			8,927.30
	(1) Basis contract volumes not included in the above table were 8.2 MMDth as of December 31, 2012.
	(2) Basis contract volumes not included in the above table were 9.2 MMDth as of December 31, 2012.
	(3) Contract volumes are from NiSource's unregulated natural gas marketing business that was sold on September 1, 2013.
Location And Fair Value Of Derivative Instruments On Consolidated Balance Sheets	'
	Asset Derivatives (in millions)	September 30,				December 31,
		2013				2012
	Balance Sheet Location	Fair Value				Fair Value
	Derivatives designated as hedging instruments
	Interest rate risk activities
	Price risk management assets (current)	$	21			$	—
	Price risk management assets (noncurrent)	—				40.4
	Total derivatives designated as hedging instruments	$	21			$	40.4
	Derivatives not designated as hedging instruments
	Commodity price risk programs
	Price risk management assets (current)	$	0.1			$	0.5
	Price risk management assets (noncurrent)	—				0.3
	Assets held for sale (current)(1)	—				107
	Total derivatives not designated as hedging instruments	$	0.1			$	107.8
	Total Asset Derivatives	$	21.1			$	148.2
	(1) Prior to the classification as "Assets held for sale," $15.3 million was classified as noncurrent.
	Liability Derivatives (in millions)	September 30,				December 31,
		2013				2012
	Balance Sheet Location	Fair Value				Fair Value
	Derivatives designated as hedging instruments
	Commodity price risk programs
	Price risk management liabilities (current)	$	0.1			$	0.1
	Price risk management liabilities (noncurrent)	—				—
	Total derivatives designated as hedging instruments	$	0.1			$	0.1
	Derivatives not designated as hedging instruments
	Commodity price risk programs
	Price risk management liabilities (current)	$	8.7			$	8.1
	Price risk management liabilities (noncurrent)	1.5				2.6
	Liabilities held for sale (current)(2)	—				104.7
	Total derivatives not designated as hedging instruments	$	10.2			$	115.4
	Total Liability Derivatives	$	10.3			$	115.5
Offsetting Assets and Liabilities	'
	Offsetting of Derivative Assets (in millions)
	As of September 30, 2013
		Gross Amounts of Recognized Assets				Gross Amounts Offset in the Statement of Financial Position				Net Amounts of Assets Presented in the Statement of Financial Position				Gross Amounts Not Offset in the Statement in the Statement of Financial Position				Net Amount
	Counterparty A (1)	$	—			$	—			$	—			$	—			$	—
	Counterparty B	0.1				—				0.1				(10.3		)		(10.2		)
	Other (2)	21				—				21				—				21
	Total	$	21.1			$	—			$	21.1			$	(10.3	)		$	10.8
	Offsetting of Derivative Liabilities (in millions)
	As of September 30, 2013
		Gross Amounts of Recognized Liabilities				Gross Amounts Offset in the Statement of Financial Position				Net Amounts of Liabilities Presented in the Statement of Financial Position				Gross Amounts Not Offset in the Statement in the Statement of Financial Position				Net Amount
	Counterparty A (1)	$	—			$	—			$	—			$	—			$	—
	Counterparty B	(10.3		)		—				(10.3		)		10.3				—
	Other (2)	—				—				—				—				—
	Total	$	(10.3	)		$	—			$	(10.3	)		$	10.3			$	—
	Offsetting of Derivative Assets (in millions)
	As of December 31, 2012
		Gross Amounts of Recognized Assets				Gross Amounts Offset in the Statement of Financial Position				Net Amounts of Assets Presented in the Statement of Financial Position				Gross Amounts Not Offset in the Statement in the Statement of Financial Position				Net Amount
	Counterparty A (1)	$	71.8			$	—			$	71.8			$	(71.8	)		$	—
	Counterparty B	0.9				—				0.9				(0.9		)		—
	Other (2)	75.5				—				75.5				—				75.5
	Total	$	148.2			$	—			$	148.2			$	(72.7	)		$	75.5
	Offsetting of Derivative Liabilities (in millions)
	As of December 31, 2012
		Gross Amounts of Recognized Liabilities				Gross Amounts Offset in the Statement of Financial Position				Net Amounts of Liabilities Presented in the Statement of Financial Position				Gross Amounts Not Offset in the Statement in the Statement of Financial Position				Net Amount
	Counterparty A (1)	$	(103.4	)		$	—			$	(103.4	)		$	71.8			$	(31.6	)
	Counterparty B	(10.8		)		—				(10.8		)		0.9				(9.9		)
	Other (2)	(1.3		)		—				(1.3		)		—				(1.3		)
	Total	$	(115.5	)		$	—			$	(115.5	)		$	72.7			$	(42.8	)
	(1) Amounts in "Counterparty A" are balances from the commercial and industrial natural gas portfolio of NiSource's unregulated natural gas marketing business which was sold on September 1, 2013, and are included in assets and liabilities held for sale. Refer to Note 4, "Discontinued Operations and Assets and Liabilities Held for Sale" for additional information regarding the transaction.
	(2) Amounts in "Other" include physical positions with counterparties that are part of NiSource's unregulated natural gas marketing business as well as fixed-to-variable interest rate swap agreements entered into by NiSource.
Schedule of Derivative Instruments, Effect on Other Comprehensive Income (Loss)	'
	Three Months Ended (in millions)
		Amount of Gain								Location of Loss		Amount of Loss
		Recognized in OCI on								Reclassified from  AOCI		Reclassified from AOCI
		Derivative (Effective								into Income (Effective		into Income (Effective
		Portion)								Portion)		Portion)
	Derivatives in Cash Flow	September 30,				September 30, 2012						September 30,				September 30, 2012
	Hedging Relationships	2013										2013
	Commodity price risk programs	$	—			$	0.2			Cost of Sales		$	—			$	—
	Interest rate risk activities	—				0.4				Interest expense, net		(0.4		)		(0.7		)
	Total	$	—			$	0.6					$	(0.4	)		$	(0.7	)
	Nine Months Ended (in millions)
		Amount of Gain								Location of Gain  (Loss)		Amount of Gain (Loss)
		Recognized in OCI on								Reclassified from  AOCI		Reclassified from AOCI
		Derivative (Effective								into Income (Effective		into Income (Effective
		Portion)								Portion)		Portion)
	Derivatives in Cash Flow	September 30,				September 30, 2012						September 30,				September 30, 2012
	Hedging Relationships	2013										2013
	Commodity price risk programs	$	—			$	0.8			Cost of Sales		$	0.1			$	(0.8	)
	Interest rate risk activities	—				1.2				Interest expense, net		(1.2		)		(2.0		)
	Total	$	—			$	2					$	(1.1	)		$	(2.8	)
Schedule of Derivatives Instruments Statements of Financial Performance and Financial Position, Location	'
	Derivatives in Fair Value Hedging Relationships
	Three Months Ended (in millions)
	Derivatives in Fair Value Hedging	Location of Loss Recognized in		Amount of Loss Recognized
	Relationships	Income on Derivatives		in Income on Derivatives
				September 30, 2013				September 30, 2012
	Interest rate risk activities	Interest expense, net		$	(9.9	)		$	(8.3	)
	Total			$	(9.9	)		$	(8.3	)
	Nine Months Ended (in millions)
	Derivatives in Fair Value Hedging	Location of Loss Recognized in		Amount of Loss Recognized
	Relationships	Income on Derivatives		in Income on Derivatives
				September 30, 2013				September 30, 2012
	Interest rate risk activities	Interest expense, net		$	(19.4	)		$	(16.5	)
	Total			$	(19.4	)		$	(16.5	)
	Three Months Ended (in millions)
	Hedged Item in Fair Value Hedge	Location of Gain Recognized in		Amount of Gain Recognized
	Relationships	Income on Related Hedged Item		in Income on Related Hedged Items
				September 30, 2013				September 30, 2012
	Fixed-rate debt	Interest expense, net		$	9.9			$	8.3
	Total			$	9.9			$	8.3
	Nine Months Ended (in millions)
	Hedged Item in Fair Value Hedge	Location of Gain Recognized in		Amount of Gain Recognized
	Relationships	Income on Related Hedged Item		in Income on Related Hedged Items
				September 30, 2013				September 30, 2012
	Fixed-rate debt	Interest expense, net		$	19.4			$	16.5
	Total			$	19.4			$	16.5
	Derivatives not designated as hedging instruments
	Three Months Ended (in millions)
	Derivatives Not Designated as Hedging	Location of Gain (Loss)		Amount of Realized/Unrealized Gain
	Instruments	Recognized in		(Loss) Recognized in Income on
		Income on Derivatives		Derivatives *
				September 30, 2013				September 30, 2012
	Commodity price risk programs	Gas Distribution revenues		$	—			$	—
	Commodity price risk programs	Other revenues		—				—
	Commodity price risk programs	Cost of Sales		6.6				6.8
	Commodity price risk programs	(Loss) Income from Discontinued Operations - net of taxes		(1.2		)		0.6
	Total			$	5.4			$	7.4
	* For the amounts of realized/unrealized gain (loss) recognized in income on derivatives disclosed in the table above, gains of $6.7 million and $6.8 million for the three months ended September 30, 2013 and 2012, respectively, were deferred as allowed per regulatory orders. These amounts will be amortized to income over future periods of up to twelve months as specified in a regulatory order.
	Nine Months Ended (in millions)
	Derivatives Not Designated as Hedging	Location of Gain (Loss)		Amount of Realized/Unrealized Gain
	Instruments	Recognized in		(Loss) Recognized in Income on
		Income on Derivatives		Derivatives *
				September 30, 2013				September 30, 2012
	Commodity price risk programs	Gas Distribution revenues		$	—			$	0.3
	Commodity price risk programs	Other revenues		—				—
	Commodity price risk programs	Cost of Sales		7.5				(8.6		)
	Commodity price risk programs	(Loss) Income from Discontinued Operations - net of taxes		(0.8		)		2.8
	Total			$	6.7			$	(5.5	)
	* For the amounts of realized/unrealized gain (loss) recognized in income on derivatives disclosed in the table above, a gain of $7.6 million for the nine months ended September 30, 2013 and a loss of $8.3 million for the nine months ended 2012 were deferred as allowed per regulatory orders. These amounts will be amortized to income over future periods of up to twelve months as specified in a regulatory order.

Fair_Value_Disclosures_Tables

Fair Value Disclosures (Tables)	9 Months Ended
	Sep. 30, 2013
Fair Value Disclosures [Abstract]	'
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	'
	Recurring Fair Value Measurements	Quoted Prices in		Significant		Significant			Balance as of September 30, 2013
	September 30, 2013 (in millions)	Active Markets		Other		Unobservable
		for Identical		Observable		Inputs
		Assets		Inputs		(Level 3)
		(Level 1)		(Level 2)
	Assets
	Commodity Price risk management assets:
	Physical price risk programs	$	—	$	—	$	—		$	—
	Financial price risk programs	0.1				—			0.1
	Interest rate risk activities	—		21		—			21
	Available-for-sale securities	26.5		99.9		—			126.4
	Total	$	26.6	$	120.9	$	—		$	147.5
	Liabilities
	Commodity Price risk management liabilities:
	Physical price risk programs	$	—	$	—	$	—		$	—
	Financial price risk programs	9.7		—		0.6			10.3
	Total	$	9.7	$	—	$	0.6		$	10.3
	Recurring Fair Value Measurements	Quoted Prices in		Significant		Significant			Balance as of
	December 31, 2012 (in millions)	Active Markets		Other		Unobservable			December 31, 2012
		for Identical		Observable		Inputs
		Assets		Inputs		(Level 3)
		(Level 1)		(Level 2)
	Assets
	Commodity Price risk management assets:
	Physical price risk programs	$	—	$	—	$	—		$	—
	Physical price risk programs (assets held for sale)	—		35.4		—			35.4
	Financial price risk programs	0.7		—		0.1			0.8
	Financial price risk programs (assets held for sale)	70.8		0.8		—			71.6
	Interest rate risk activities	—		40.4		—			40.4
	Available-for-sale securities	27.4		84.4		—			111.8
	Total	$	98.9	$	161	$	0.1		$	260
	Liabilities
	Commodity Price risk management liabilities:
	Physical price risk programs	$	—	$	—	$	—		$	—
	Financial price risk programs	10.8		—		—			10.8
	Financial price risk programs (liabilities held for sale)	104.2		0.5		—			104.7
	Total	$	115	$	0.5	$	—		$	115.5
Available-For-Sale Debt Securities	'
	The amortized cost, gross unrealized gains and losses, and fair value of available-for-sale debt securities at September 30, 2013 and December 31, 2012 were:
	(in millions)	Amortized		Gross Unrealized Gains		Gross Unrealized Losses			Fair
		Cost							Value
	Available-for-sale debt securities, September 30, 2013
	U.S. Treasury	$	31.3	$	0.5	$	(0.3	)	$	31.5
	Corporate/Other	94.8		1.2		(1.1		)	94.9
	Total Available-for-sale debt securities	$	126.1	$	1.7	$	(1.4	)	$	126.4
	(in millions)	Amortized		Gross Unrealized Gains		Gross Unrealized Losses			Fair
		Cost							Value
	Available-for-sale debt securities, December 31, 2012
	U.S. Treasury	$	31.1	$	1.5	$	—		$	32.6
	Corporate/Other	76.8		2.5		(0.1		)	79.2
	Total Available-for-sale debt securities	$	107.9	$	4	$	(0.1	)	$	111.8
Carrying Amount And Estimated Fair Values Of Financial Instruments	'
	(in millions)	Carrying		Estimated Fair		Carrying			Estimated Fair
		Amount as of		Value as of		Amount as of			Value as of
		September 30, 2013		September 30, 2013		Dec. 31, 2012			Dec. 31, 2012
	Long-term debt (including current portion)	$	7,630.30	$	8,172.10	$	7,326.30		$	8,389.00

Transfers_Of_Financial_Assets_

Transfers Of Financial Assets (Tables)	9 Months Ended
	Sep. 30, 2013
Transfers and Servicing [Abstract]	'
Schedule Of Gross And Net Receivables Transferred As Well As Short-Term Borrowings Related To The Securitization Transactions	'
	The following table reflects the gross and net receivables transferred as well as short-term borrowings related to the securitization transactions as of September 30, 2013 and December 31, 2012 for Columbia of Ohio, Northern Indiana and Columbia of Pennsylvania:
	(in millions)	September 30, 2013		31-Dec-12
	Gross Receivables	$	350.8	$	525.3
	Less: Receivables not transferred	142.5		292
	Net receivables transferred	$	208.3	$	233.3
	Short-term debt due to asset securitization	$	208.3	$	233.3

Pension_And_Other_Postretireme1

Pension And Other Postretirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2013
Pension and Other Postretirement Benefit Expense [Abstract]	'
Components Of The Plans' Net Periodic Benefits Cost	'
		Pension Benefits								Other Postretirement
										Benefits
	Three Months Ended September 30, (in millions)	2013				2012				2013			2012
	Components of Net Periodic Benefit Cost
	Service cost	$	9			$	9.4			$	3		$	2.8
	Interest cost	24.9				28.2				8			9.6
	Expected return on assets	(42.0		)		(41.2		)		(7.6		)	(6.7		)
	Amortization of transition obligation	—				—				0.2			0.3
	Amortization of prior service cost	—				0.1				(0.2		)	0.5
	Recognized actuarial loss	18.9				20.3				2.8			2.3
	Settlement loss	4				1.9				—			—
	Total Net Periodic Benefit Costs	$	14.8			$	18.7			$	6.2		$	8.8
		Pension Benefits								Other Postretirement
										Benefits
	Nine Months Ended September 30, (in millions)	2013				2012				2013			2012
	Components of Net Periodic Benefit Cost
	Service cost	$	27.7			$	28.2			$	9		$	8.4
	Interest cost	73.5				84.6				24.2			28.2
	Expected return on assets	(126.5		)		(123.4		)		(22.8		)	(20.1		)
	Amortization of transition obligation	—				—				0.4			0.9
	Amortization of prior service cost	0.2				0.3				(0.6		)	0.3
	Recognized actuarial loss	59.3				60.9				8.4			7.1
	Settlement loss	28.3				1.9				—			—
	Total Net Periodic Benefit Costs	$	62.5			$	52.5			$	18.6		$	24.8
Schedule of Assumptions Used	'
		31-Aug-13			31-May-13			28-Feb-13			31-Dec-12
	Actuarial Assumptions
	Discount Rate	4.25	%		3.75	%		3.5	%		3.63	%
	Expected return on assets	8.3	%		8.3	%		8.3	%		8.3	%

ShortTerm_Borrowings_Tables

Short-Term Borrowings (Tables)	9 Months Ended
	Sep. 30, 2013
Short-term Debt [Abstract]	'
Schedule Of Short-Term Borrowings	'
	(in millions)	September 30,		December 31,
		2013		2012
	Commercial Paper weighted average interest rate of 0.67% and 1.11% at September 30, 2013 and December 31, 2012, respectively.	$	612.5	$	499.6
	Credit facilities borrowings weighted average interest rate of 3.73% at December 31, 2012.	—		44
	Accounts receivable securitization facility borrowings	208.3		233.3
	Total short-term borrowings	$	820.8	$	776.9

Other_Commitments_And_Continge1

Other Commitments And Contingencies (Tables)	9 Months Ended
	Sep. 30, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Existence And Expiration Of Commercial Commitments	'
	The total guarantees and indemnities in existence at September 30, 2013 and the years in which they expire were:
	(in millions)	Total		2013		2014		2015		2016		2017		After
	Guarantees of subsidiaries debt	$	7,210.50	$	—	$	500	$	230	$	616.5	$	507	$	5,357.00
	Guarantees supporting commodity transactions of subsidiaries	10.7		10.7		—		—		—		—		—
	Accounts receivable securitization	208.3		208.3		—		—		—		—		—
	Lines of credit	612.5		612.5		—		—		—		—		—
	Letters of credit	39.2		0.7		22.3		16.2		—		—		—
	Other guarantees	132.3		18.1		48.4		3		—		—		62.8
	Total commercial commitments	$	8,213.50	$	850.3	$	570.7	$	249.2	$	616.5	$	507	$	5,419.80

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Loss (Tables)	9 Months Ended
	Sep. 30, 2013
Components of Accumulated Other Comprehensive Income (Loss) [Abstract]	'
Components Of Accumulated Other Comprehensive Loss	'
	Three Months Ended September 30, 2013 (in millions)	Gains and Losses on Securities(1)			Gains and Losses on Cash Flow Hedges(1)			Pension and OPEB Items(1)			Accumulated
											Other
											Comprehensive
											Loss(1)
	Balance as of July 1, 2013	$	(0.7	)	$	(27.2	)	$	(34.1	)	$	(62.0	)
	Other comprehensive income before reclassifications	1			(0.1		)	(0.6		)	0.3
	Amounts reclassified from accumulated other comprehensive income	(0.1		)	0.7			0.7			1.3
	Net current-period other comprehensive income	0.9			0.6			0.1			1.6
	Balance as of September 30, 2013	$	0.2		$	(26.6	)	$	(34.0	)	$	(60.4	)
	Nine Months Ended September 30, 2013 (in millions)	Gains and Losses on Securities(1)			Gains and Losses on Cash Flow Hedges(1)			Pension and OPEB Items(1)			Accumulated
											Other
											Comprehensive
											Loss(1)
	Balance as of January 1, 2013	$	2.6		$	(28.6	)	$	(39.5	)	$	(65.5	)
	Other comprehensive income before reclassifications	(1.9		)	(0.1		)	2.6			0.6
	Amounts reclassified from accumulated other comprehensive income	(0.5		)	2.1			2.9			4.5
	Net current-period other comprehensive (loss) income	(2.4		)	2			5.5			5.1
	Balance as of September 30, 2013	$	0.2		$	(26.6	)	$	(34.0	)	$	(60.4	)
	(1)All amounts are net of tax. Amounts in parentheses indicate debits.

Business_Segment_Information_T

Business Segment Information (Tables)	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Schedule Of Operating Income Derived From Revenues And Expenses By Segment	'
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
	(in millions)	2013			2012			2013			2012
	REVENUES
	Gas Distribution Operations
	Unaffiliated	$	409.5		$	378.9		$	2,126.80		$	1,882.80
	Intersegment	—			0.1			0.2			0.4
	Total	409.5			379			2,127.00			1,883.20
	Columbia Pipeline Group Operations
	Unaffiliated	251.3			156.6			752			599.1
	Intersegment	31.4			31.5			105.9			105.4
	Total	282.7			188.1			857.9			704.5
	Electric Operations
	Unaffiliated	413.6			418.3			1,175.90			1,148.40
	Intersegment	0.1			0.2			0.5			0.6
	Total	413.7			418.5			1,176.40			1,149.00
	Corporate and Other
	Unaffiliated	2.4			2.4			5.8			7
	Intersegment	119.6			119.3			351.3			345.3
	Total	122			121.7			357.1			352.3
	Eliminations	(151.1		)	(151.1		)	(457.9		)	(451.7		)
	Consolidated Gross Revenues	$	1,076.80		$	956.2		$	4,060.50		$	3,637.30
	Operating Income (Loss)
	Gas Distribution Operations	$	(5.0	)	$	10.4		$	279.1		$	263.4
	Columbia Pipeline Group Operations	98.7			38.8			321			268.9
	Electric Operations	87.5			83.7			212.2			200.2
	Corporate and Other	(4.8		)	(1.4		)	(13.0		)	1
	Consolidated Operating Income	$	176.4		$	131.5		$	799.3		$	733.5

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2013
Supplemental Cash Flow Information [Abstract]	'
Additional Information Regarding Condensed Statements Of Consolidated Cash Flows	'
		Nine Months Ended
		September 30,
	(in millions)	2013		2012
	Supplemental Disclosures of Cash Flow Information
	Non-cash transactions:
	Capital expenditures included in current liabilities	$	202.7	$	119.6
	Stock issuance to employee savings plans	22.2		19.4
	Schedule of interest and income taxes paid:
	Cash paid for interest, net of interest capitalized amounts	$	359.4	$	336.1
	Cash paid for income taxes	8.5		8.4

Earnings_Per_Share_Table_Detai

Earnings Per Share Table (Details)	3 Months Ended		9 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]	'	'	'	'
Basic Average Common Shares Outstanding	312,842	290,328	312,053	285,891
Nonqualified stock options	112	197	102	159
Shares contingently issuable under employee stock plans	369	434	327	393
Shares restricted under stock plans	490	654	477	626
Forward Agreements	0	8,399	0	9,609
Weighted Average Number of Shares Outstanding, Diluted	313,813	300,012	312,959	296,678

Recovered_Sheet1

Discontinued Operations and Assets and Liabilities Held for Sale (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Discontinued Operations And Assets And Liabilities Held For Sale [Abstract]	'	'	'	'
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	($1.50)	$0	$34.90	$0

Recovered_Sheet2

Discontinued Operations and Assets and Liabilities Held for Sale (Assets and Liabilities Table) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets and Liabilities of Discontinued Operations and Held For Sale [Line Items]	'	'
Disposal Group, Including Discontinued Operation, Property, Plant, and Equipment, Net	'	$21.50
Disposal Group Including Discontinued Operation, Price Risk Management Assets	'	107
Disposal Group, Including Discontinued Operation, Other Assets	'	5.4
Assets of Disposal Group, Including Discontinued Operation	0	133.9
Disposal Group Including Discontinued Operation, Price Risk Management Liabilities	'	104.7
Disposal Group, Including Discontinued Operation, Other Liabilities	'	3.9
Liabilities of Disposal Group, Including Discontinued Operation	0	108.6
Gas Distribution Operations [Member]	'	'
Assets and Liabilities of Discontinued Operations and Held For Sale [Line Items]	'	'
Disposal Group, Including Discontinued Operation, Property, Plant, and Equipment, Net	'	21.5
Disposal Group Including Discontinued Operation, Price Risk Management Assets	'	0
Disposal Group, Including Discontinued Operation, Other Assets	'	4.5
Assets of Disposal Group, Including Discontinued Operation	'	26
Disposal Group Including Discontinued Operation, Price Risk Management Liabilities	'	0
Disposal Group, Including Discontinued Operation, Other Liabilities	'	3.3
Liabilities of Disposal Group, Including Discontinued Operation	'	3.3
Electric Operations [Member]	'	'
Assets and Liabilities of Discontinued Operations and Held For Sale [Line Items]	'	'
Disposal Group, Including Discontinued Operation, Property, Plant, and Equipment, Net	'	0
Disposal Group Including Discontinued Operation, Price Risk Management Assets	'	0
Disposal Group, Including Discontinued Operation, Other Assets	'	0.7
Assets of Disposal Group, Including Discontinued Operation	'	0.7
Disposal Group Including Discontinued Operation, Price Risk Management Liabilities	'	0
Disposal Group, Including Discontinued Operation, Other Liabilities	'	0.6
Liabilities of Disposal Group, Including Discontinued Operation	'	0.6
Corporate and Other [Member]	'	'
Assets and Liabilities of Discontinued Operations and Held For Sale [Line Items]	'	'
Disposal Group, Including Discontinued Operation, Property, Plant, and Equipment, Net	'	0
Disposal Group Including Discontinued Operation, Price Risk Management Assets	'	107
Disposal Group, Including Discontinued Operation, Other Assets	'	0.2
Assets of Disposal Group, Including Discontinued Operation	'	107.2
Disposal Group Including Discontinued Operation, Price Risk Management Liabilities	'	104.7
Disposal Group, Including Discontinued Operation, Other Liabilities	'	0
Liabilities of Disposal Group, Including Discontinued Operation	'	$104.70

Discontinued_Operations_And_As2

Discontinued Operations And Assets And Liabilities Held For Sale (Summary Of Gain (Loss) On Disposition Of Discontinued Operations Net Of Taxes) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Discontinued Operations And Assets And Liabilities Held For Sale [Abstract]	'	'	'	'
Revenues from Discontinued Operations	$0.40	$10.80	$1.30	$28.80
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax, Total	0.1	4.5	12.2	8.6
Discontinued Operation, Tax Effect of Discontinued Operation	0	1.8	4.7	3.2
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	0.1	2.7	7.5	5.4
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	($1.50)	$0	$34.90	$0

Asset_Retirement_Obligations_C

Asset Retirement Obligations (Changes In Company's Liability For Asset Retirement Obligations) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Beginning Balance	$160.40	$146.40
Accretion expense	0.9	0.8
Accretion recorded as a regulatory asset	6.5	6.6
Additions	9.7	0
Settlements	-1.3	-0.7
Change in estimated cash flows	-0.7	-1.1
Ending Balance	$175.50	$152

Regulatory_Matters_Narrative_D

Regulatory Matters (Narrative) (Details) (USD $)

3 Months Ended

9 Months Ended

0 Months Ended

3 Months Ended

Jun. 30, 2013

Dec. 31, 2013

Apr. 15, 2013

Feb. 28, 2013

23-May-13

Sep. 28, 2012

Sep. 30, 2013

Oct. 10, 2013

Oct. 03, 2013

Aug. 01, 2013

Jul. 19, 2013

Apr. 30, 2013

Apr. 24, 2013

Jul. 03, 2013

Sep. 23, 2013

Feb. 27, 2013

Sep. 03, 2013

Apr. 16, 2013

Mar. 07, 2013

Mar. 31, 2013

Jun. 03, 2013

Jan. 24, 2013

29-May-13

Columbia Of Ohio [Member]

Columbia Of Ohio [Member]

Columbia Of Ohio [Member]

Columbia Of Ohio [Member]

Columbia Of Pennsylvania [Member]

Columbia Of Pennsylvania [Member]

Northern Indiana [Member]

Northern Indiana [Member]

Northern Indiana [Member]

Northern Indiana [Member]

Northern Indiana [Member]

Northern Indiana [Member]

Northern Indiana [Member]

Columbia Of Virginia [Member]

Columbia Of Maryland [Member]

Columbia Of Maryland [Member]

Columbia Of Massachusetts [Member]

Columbia Of Massachusetts [Member]

Columbia Of Massachusetts [Member]

Columbia Transmission [Member]

Columbia Transmission [Member]

Columbia Transmission [Member]

Columbia of Kentucky [Member]

Customer Settlement [Member]

Customer Settlement [Member]

Customer Settlement [Member]

Regulatory Matters [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proposed Reduction of PIPP Rider

'

'

$6,700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proposed Reduction to Uncollectible Expense Rider

'

'

16,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Base Chip Transition Cost

8,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Capital Expenditure Program Expenditures

'

8,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proposed Revenue Increase

'

'

'

29,000,000

'

77,300,000

'

'

'

'

'

'

'

'

'

5,300,000

29,500,000

30,100,000

'

'

'

'

16,600,000

MASSPOWER Settlement

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

8,900,000

'

'

'

'

'

'

Annual Revenue Increase

'

'

'

'

55,300,000

'

'

'

'

'

'

'

'

'

3,600,000

'

'

'

'

'

'

'

'

Decoupling Revenue

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10,500,000

'

'

'

'

Annual Investment in SAVE Plan

'

'

'

'

'

'

'

'

'

'

'

'

'

25,000,000

'

'

'

'

'

'

'

'

'

Increase to Annual Investment in SAVE Plan

'

'

'

'

'

'

'

'

'

'

'

'

'

5,000,000

'

'

'

'

'

'

'

'

'

Five-year Period Modernization Investment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,500,000,000

'

Initial Customer Refund

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

50,000,000

'

Customer Refund

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

88,100,000

'

'

'

Capital Cost Recovery Mechanism Revenue Requirement

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

14.00%

'

Required Annual Capital Maintenance Expenditure

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100,000,000

'

Annual Capital Cost Recovery Mechanism Limit

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

300,000,000

'

Annual Capital Cost Recovery Mechanism Limit Tolerance

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15.00%

'

Total Capital Cost Recovery Mechanism Over Five-year Term

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,500,000,000

'

Average Construction Work in Progress

'

'

'

'

'

'

19,800,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Transmission Assets Revenue

'

'

'

'

'

'

2,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Depreciation Rate Reduction

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.50%

'

Annual base rate reduction effective January 1, 2014

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

25,000,000

'

LNG Peaking Facility Investment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

30,000,000

'

'

Eligible Costs Recovered Under TDSIC

'

'

'

'

'

'

'

'

'

'

'

80.00%

'

'

'

'

'

'

'

'

'

'

'

Recoverable Costs Deferred for Future Recovery Under TDSIC

'

'

'

'

'

'

'

'

'

'

'

20.00%

'

'

'

'

'

'

'

'

'

'

'

Seven Year Plan of Eligible Investments Under TDSIC

'

'

'

'

'

'

'

'

710,000,000

'

1,100,000,000

'

'

'

'

'

'

'

'

'

'

'

'

MATS Compliance Projects Capital Costs

'

'

'

'

'

'

'

59,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

ECR-21 Net Capital Expenditures

'

'

'

'

'

'

'

'

'

'

'

'

376,400,000

'

'

'

'

'

'

'

'

'

'

ECR-22 Net Capital Expenditures

'

'

'

'

'

'

'

'

'

478,800,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Change in ECR Net Capital Expenditures

'

'

'

'

'

'

'

'

'

$102,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Risk_Management_Activities_Nar

Risk Management Activities (Narrative) (Details) (USD $)	0 Months Ended		9 Months Ended			12 Months Ended				9 Months Ended
	Sep. 16, 2005	Jul. 22, 2003	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2012	Sep. 16, 2005	Sep. 16, 2005	Sep. 30, 2013	Sep. 30, 2012
						Physical Sales Contracts Marked-To-Market [Member]	Financial Derivative Contracts Marked To Market [Member]	5.25% - Due September 15, 2017 [Member]	5.45% - Due September 15, 2020 [Member]	Millennium Pipeline Company, L.L.C [Member]	Millennium Pipeline Company, L.L.C [Member]
Derivative Instruments Gain Loss [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	'	'	$0	$0	'	'	'	'	'	'	'
Additional Collateral, Aggregate Fair Value	'	'	800,000	'	'	'	'	'	'	'	'
Face amount of notes	'	'	'	'	'	'	'	1,000,000,000	1,000,000,000	'	'
Fair value of physical sales contracts and derivative contracts	'	'	'	'	'	35,400,000	-33,200,000	'	'	'	'
Outstanding debt	'	'	7,200,000,000	'	'	'	'	'	'	'	'
Outstanding debt subject to interest rate fluctuations	'	'	500,000,000	'	'	'	'	'	'	'	'
Derivative, Notional Amount	900,000,000	500,000,000	'	'	'	'	'	'	'	'	'
Number of counterparties in swap agreement	'	4	'	'	'	'	'	'	'	'	'
Fixed interest rate under swap agreement	'	5.40%	'	'	'	'	'	'	'	'	'
Floating interest amount, average interest addition	'	0.78%	'	'	'	'	'	'	'	'	'
Number of counterparties in swap agreement settled	6	'	'	'	'	'	'	'	'	'	'
Payment for settlement of interest rate swap	35,500,000	'	'	'	'	'	'	'	'	'	'
Forward starting interest rate swap settlement amount	'	'	8,600,000	'	'	'	'	'	'	'	'
Percentage of interest in Millennium	'	'	47.50%	'	'	'	'	'	'	47.50%	'
Loss recognized in income statement classified in accumulated other comprehensive income(loss)	'	'	100,000	'	'	'	'	'	'	'	'
Cash on deposit with brokers for margin requirements	'	'	13,500,000	'	45,700,000	'	'	'	'	'	'
Interest rate on debt	'	'	'	'	'	'	'	5.25%	5.45%	'	'
Debt Instrument, Interest Rate, Effective Percentage	'	'	'	'	'	'	'	5.67%	5.88%	'	'
Other Comprehensive Income Unrecognized Gain Loss On Derivatives Arising During Period Net Of Tax	'	'	'	'	'	'	'	'	'	$17,900,000	$18,700,000

Risk_Management_Activities_Com

Risk Management Activities (Commodity Price Risk Program Derivative Contracted Gross Volumes) (Details)	9 Months Ended		12 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Gas Price Volatility Program [Member]	'		'
Derivative [Line Items]	'		'
Commodity price risk program derivative contracted gross volumes, MMDth	25,800,000		26,300,000
Price Protection Service Program [Member]	'		'
Derivative [Line Items]	'		'
Commodity price risk program derivative contracted gross volumes, MMDth	1,000,000		1,200,000
DependaBill Program [Member]	'		'
Derivative [Line Items]	'		'
Commodity price risk program derivative contracted gross volumes, MMDth	300,000		300,000
Gas Marketing Program [Member]	'		'
Derivative [Line Items]	'		'
Commodity price risk program derivative contracted gross volumes, MMDth	0	[1],[2]	9,100,000	[1],[2]
Basis contract volumes, MMDth	'		8,200,000
Gas Marketing Forward Physical Derivatives [Member]	'		'
Derivative [Line Items]	'		'
Commodity price risk program derivative contracted gross volumes, MMDth	0	[1],[3]	8,400,000	[1],[3]
Basis contract volumes, MMDth	'		9,200,000
Electric Energy Program [Member]	'		'
Derivative [Line Items]	'		'
Commodity price risk program derivative contracted gross volumes, MMDth	1,218,200,000		8,927,300,000
[1]	Contract volumes are from NiSource's unregulated natural gas marketing business that was sold on September 1, 2013.
[2]	Basis contract volumes not included in the above table were 8.2 MMDth as of DecemberB 31, 2012.
[3]	Basis contract volumes not included in the above table were 9.2 MMDth as of DecemberB 31, 2012.

Risk_Management_Activities_Loc

Risk Management Activities (Location And Fair Value Of Derivative Instruments On Consolidated Balance Sheets) (Details) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Derivatives, Fair Value [Line Items]	'		'
Total Asset Derivatives	$21.10		$148.20
Total Liability Derivatives	10.3		115.5
Designated As Hedging Instruments [Member] | Interest Rate Risk Activities [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Asset Derivatives	21		40.4
Designated As Hedging Instruments [Member] | Interest Rate Risk Activities [Member] | Price Risk Management Assets (Current) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Asset Derivatives	21		0
Designated As Hedging Instruments [Member] | Interest Rate Risk Activities [Member] | Price Risk Management Assets (Noncurrent) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Asset Derivatives	0		40.4
Designated As Hedging Instruments [Member] | Commodity Price Risk Programs [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Liability Derivatives	0.1		0.1
Designated As Hedging Instruments [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities (Current) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Liability Derivatives	0.1		0.1
Designated As Hedging Instruments [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities (Noncurrent) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Liability Derivatives	0		0
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Asset Derivatives	0.1		107.8
Total Liability Derivatives	10.2		115.4
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Assets (Current) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Asset Derivatives	0.1		0.5
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Assets (Noncurrent) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Asset Derivatives	0		0.3
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities (Current) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Liability Derivatives	8.7		8.1
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities (Noncurrent) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Liability Derivatives	1.5		2.6
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Assets Held For Sale [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Asset Derivatives	0	[1]	107	[1]
Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities Held For Sale [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Liability Derivatives	0	[2]	104.7	[2]
Previous [Member] | Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Assets (Noncurrent) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Asset Derivatives	'		15.3
Previous [Member] | Not Designated as Hedging Instrument [Member] | Commodity Price Risk Programs [Member] | Price Risk Management Liabilities (Noncurrent) [Member]	'		'
Derivatives, Fair Value [Line Items]	'		'
Total Liability Derivatives	'		$17.70
[1]	Prior to the classification as "Assets held for sale," $15.3 million was classified as noncurrent.
[2]	Prior to the classification as "Liabilities held for sale," $17.7 million was classified as noncurrent.

Risk_Management_Activities_Ris

Risk Management Activities Risk Management Activities (Offsetting Assets and Liabilities) (Details) (USD $)	Sep. 30, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Offsetting Assets and Liabilities [Line Items]	'		'
Gross Amounts of Recognized Assets	$21.10		$148.20
Gross Amounts Offset in the Statement of Financial Position	0		0
Net Amounts of Assets Presented in the Statement of Financial Position	21.1		148.2
Gross Amounts Not Offset in the Statement of Financial Position	-10.3		-72.7
Net Derivative Position - Assets	10.8		75.5
Gross Amounts of Recognized Liabilities	-10.3		-115.5
Gross Amounts Offset in the Statement of Financial Position-Liabilities	0		0
Net Amounts of Liabilities Presented in the Statement of Financial Position	-10.3		-115.5
Gross Amounts Not Offset in the Statement of Financial Position- Liabilities	10.3		72.7
Net Derivative Position-Liabilities	0		-42.8
Counterparty A [Member]	'		'
Offsetting Assets and Liabilities [Line Items]	'		'
Gross Amounts of Recognized Assets	0	[1]	71.8	[1]
Gross Amounts Offset in the Statement of Financial Position	0	[1]	0	[1]
Net Amounts of Assets Presented in the Statement of Financial Position	0	[1]	71.8	[1]
Gross Amounts Not Offset in the Statement of Financial Position	0	[1]	-71.8	[1]
Net Derivative Position - Assets	0	[1]	0	[1]
Gross Amounts of Recognized Liabilities	0	[1]	-103.4	[1]
Gross Amounts Offset in the Statement of Financial Position-Liabilities	0	[1]	0	[1]
Net Amounts of Liabilities Presented in the Statement of Financial Position	0	[1]	-103.4	[1]
Gross Amounts Not Offset in the Statement of Financial Position- Liabilities	0	[1]	71.8	[1]
Net Derivative Position-Liabilities	0	[1]	-31.6	[1]
Counterparty B [Member]	'		'
Offsetting Assets and Liabilities [Line Items]	'		'
Gross Amounts of Recognized Assets	0.1		0.9
Gross Amounts Offset in the Statement of Financial Position	0		0
Net Amounts of Assets Presented in the Statement of Financial Position	0.1		0.9
Gross Amounts Not Offset in the Statement of Financial Position	-10.3		-0.9
Net Derivative Position - Assets	-10.2		0
Gross Amounts of Recognized Liabilities	-10.3		-10.8
Gross Amounts Offset in the Statement of Financial Position-Liabilities	0		0
Net Amounts of Liabilities Presented in the Statement of Financial Position	-10.3		-10.8
Gross Amounts Not Offset in the Statement of Financial Position- Liabilities	10.3		0.9
Net Derivative Position-Liabilities	0		-9.9
Counterparty Other [Member]	'		'
Offsetting Assets and Liabilities [Line Items]	'		'
Gross Amounts of Recognized Assets	21	[2]	75.5	[2]
Gross Amounts Offset in the Statement of Financial Position	0	[2]	0	[2]
Net Amounts of Assets Presented in the Statement of Financial Position	21	[2]	75.5	[2]
Gross Amounts Not Offset in the Statement of Financial Position	0	[2]	0	[2]
Net Derivative Position - Assets	21	[2]	75.5	[2]
Gross Amounts of Recognized Liabilities	0	[2]	-1.3	[2]
Gross Amounts Offset in the Statement of Financial Position-Liabilities	0	[2]	0	[2]
Net Amounts of Liabilities Presented in the Statement of Financial Position	0	[2]	-1.3	[2]
Gross Amounts Not Offset in the Statement of Financial Position- Liabilities	0	[2]	0	[2]
Net Derivative Position-Liabilities	$0	[2]	($1.30)	[2]
[1]	Amounts in "Counterparty A" are balances from the commercial and industrial natural gas portfolio of NiSource's unregulated natural gas marketing business which was sold on September 1, 2013, and are included in assets and liabilities held for sale. Refer to Note 4, "Discontinued Operations and Assets and Liabilities Held for Sale" for additional information regarding the transaction.
[2]	Amounts in "Other" include physical positions with counterparties that are part of NiSource's unregulated natural gas marketing business as well as fixed-to-variable interest rate swap agreements entered into by NiSource.

Risk_Management_Activities_The

Risk Management Activities (The Effect Of Derivative Instruments Reclassified To Statements Of Consolidated Income) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Cash Flow Hedging [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	$0	$0.60	$0	$2
Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net, Total	-0.4	-0.7	-1.1	-2.8
Fair Value Hedging [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in Income on Derivatives	-9.9	-8.3	-19.4	-16.5
Amount of Gain (Loss) Recognized in Income on Related Hedged Items	9.9	8.3	19.4	16.5
Not Designated as Hedging Instrument [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in Income on Derivatives	5.4	7.4	6.7	-5.5
Interest Expense [Member] | Cash Flow Hedging [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net, Total	-0.4	-0.7	-1.2	-2
Cost Of Sales [Member] | Cash Flow Hedging [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net, Total	0	0	0.1	-0.8
Commodity Price Risk Programs [Member] | Cash Flow Hedging [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	0	0.2	0	0.8
Commodity Price Risk Programs [Member] | Not Designated as Hedging Instrument [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Derivative Instruments Gain (Loss) Regulatory Deferred	6.7	6.8	7.6	-8.3
Commodity Price Risk Programs [Member] | Gas Distribution Revenues [Member] | Not Designated as Hedging Instrument [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in Income on Derivatives	0	0	0	0.3
Commodity Price Risk Programs [Member] | Other Revenues [Member] | Not Designated as Hedging Instrument [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in Income on Derivatives	0	0	0	0
Commodity Price Risk Programs [Member] | Cost Of Sales [Member] | Not Designated as Hedging Instrument [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in Income on Derivatives	6.6	6.8	7.5	-8.6
Commodity Price Risk Programs [Member] | (Loss) Income From Discontinued Operations [Member] | Not Designated as Hedging Instrument [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in Income on Derivatives	-1.2	0.6	-0.8	2.8
Interest Rate Risk Activities [Member] | Cash Flow Hedging [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	0	0.4	0	1.2
Interest Rate Risk Activities [Member] | Interest Expense [Member] | Fair Value Hedging [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in Income on Derivatives	-9.9	-8.3	-19.4	-16.5
Fixed Rate Debt Hedges [Member] | Interest Expense [Member] | Fair Value Hedging [Member]	'	'	'	'
Derivative Instruments Gain Loss [Line Items]	'	'	'	'
Amount of Gain (Loss) Recognized in Income on Related Hedged Items	$9.90	$8.30	$19.40	$16.50

Fair_Value_Disclosures_Narrati

Fair Value Disclosures (Narrative) (Details) (USD $)	Mar. 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
In Millions, unless otherwise specified		Government [Member]	Government [Member]	Government [Member]	Government [Member]	Corporate/Other Bonds [Member]	Corporate/Other Bonds [Member]	Corporate/Other Bonds [Member]	Corporate/Other Bonds [Member]
Fair Value Disclosure [Line Items]	'	'	'	'	'	'	'	'	'
Available-for-sale Securities, Gross Realized Gain (Loss)	'	$0.10	$0	$0.50	$0.30	$0	$0.10	$0.30	$0.10
Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value	'	0.4	'	0.4	'	3	'	3	'
Disposal Group, Including Discontinued Operation, Goodwill	$11	'	'	'	'	'	'	'	'

Fair_Value_Disclosures_Fair_Va

Fair Value Disclosures (Fair Value Of Financial Assets And Liabilities Measured On A Recurring Basis) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available-for-sale securities	$126.40	$111.80
Fair value assets measured on recurring basis, total	147.5	260
Fair value liabilities measured on recurring basis, total	10.3	115.5
Physical Price Risk Programs [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	0	0
Fair value liabilities measured on recurring basis, total	0	0
Physical Price Risk Programs [Member] | Price Risk Management Assets Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	'	35.4
Financial Price Risk Programs [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	0.1	0.8
Fair value liabilities measured on recurring basis, total	10.3	10.8
Financial Price Risk Programs [Member] | Price Risk Management Assets Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	'	71.6
Financial Price Risk Programs [Member] | Price Risk Management Liabilities Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value liabilities measured on recurring basis, total	'	104.7
Interest Rate Risk Activities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	21	40.4
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available-for-sale securities	26.5	27.4
Fair value assets measured on recurring basis, total	26.6	98.9
Fair value liabilities measured on recurring basis, total	9.7	115
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Physical Price Risk Programs [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	0	0
Fair value liabilities measured on recurring basis, derivative financial instruments	0	0
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Physical Price Risk Programs [Member] | Price Risk Management Assets Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	'	0
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Financial Price Risk Programs [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	0.1	0.7
Fair value liabilities measured on recurring basis, derivative financial instruments	9.7	10.8
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Financial Price Risk Programs [Member] | Price Risk Management Assets Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	'	70.8
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Financial Price Risk Programs [Member] | Price Risk Management Liabilities Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value liabilities measured on recurring basis, derivative financial instruments	'	104.2
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Interest Rate Risk Activities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	0	0
Significant Other Observable Inputs (Level 2) [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available-for-sale securities	99.9	84.4
Fair value assets measured on recurring basis, total	120.9	161
Fair value liabilities measured on recurring basis, total	0	0.5
Significant Other Observable Inputs (Level 2) [Member] | Physical Price Risk Programs [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	0	0
Fair value liabilities measured on recurring basis, derivative financial instruments	0	0
Significant Other Observable Inputs (Level 2) [Member] | Physical Price Risk Programs [Member] | Price Risk Management Assets Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	'	35.4
Significant Other Observable Inputs (Level 2) [Member] | Financial Price Risk Programs [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	'	0
Fair value liabilities measured on recurring basis, derivative financial instruments	0	0
Significant Other Observable Inputs (Level 2) [Member] | Financial Price Risk Programs [Member] | Price Risk Management Assets Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	'	0.8
Significant Other Observable Inputs (Level 2) [Member] | Financial Price Risk Programs [Member] | Price Risk Management Liabilities Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value liabilities measured on recurring basis, derivative financial instruments	'	0.5
Significant Other Observable Inputs (Level 2) [Member] | Interest Rate Risk Activities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	21	40.4
Significant Unobservable Inputs (Level 3) [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Available-for-sale securities	0	0
Fair value assets measured on recurring basis, total	0	0.1
Fair value liabilities measured on recurring basis, total	0.6	0
Significant Unobservable Inputs (Level 3) [Member] | Physical Price Risk Programs [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	0	0
Fair value liabilities measured on recurring basis, derivative financial instruments	0	0
Significant Unobservable Inputs (Level 3) [Member] | Physical Price Risk Programs [Member] | Price Risk Management Assets Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	'	0
Significant Unobservable Inputs (Level 3) [Member] | Financial Price Risk Programs [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	0	0.1
Fair value liabilities measured on recurring basis, derivative financial instruments	0.6	0
Significant Unobservable Inputs (Level 3) [Member] | Financial Price Risk Programs [Member] | Price Risk Management Assets Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	'	0
Significant Unobservable Inputs (Level 3) [Member] | Financial Price Risk Programs [Member] | Price Risk Management Liabilities Held For Sale [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value liabilities measured on recurring basis, derivative financial instruments	'	0
Significant Unobservable Inputs (Level 3) [Member] | Interest Rate Risk Activities [Member]	'	'
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]	'	'
Fair value assets measured on recurring basis, derivative financial instruments	$0	$0

Fair_Value_Disclosures_Availab

Fair Value Disclosures (Available-For-Sale Debt Securities) (Details) (USD $)	9 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value Disclosure [Line Items]	'	'
Amortized Cost	$126.10	$107.90
Gross Unrealized Gains	1.7	4
Gross Unrealized Losses	-1.4	-0.1
Fair Value	126.4	111.8
Government [Member]	'	'
Fair Value Disclosure [Line Items]	'	'
Amortized Cost	31.3	31.1
Gross Unrealized Gains	0.5	1.5
Gross Unrealized Losses	-0.3	0
Fair Value	31.5	32.6
Corporate/Other Bonds [Member]	'	'
Fair Value Disclosure [Line Items]	'	'
Amortized Cost	94.8	76.8
Gross Unrealized Gains	1.2	2.5
Gross Unrealized Losses	-1.1	-0.1
Fair Value	$94.90	$79.20

Fair_Value_Disclosures_Carryin

Fair Value Disclosures (Carrying Amount And Estimated Fair Values Of Financial Instruments) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]	'	'
Long-term debt (including current portion), Estimated Fair Value	$8,172.10	$8,389
Long-term debt (including current portion), Carrying Amount	$7,630.30	$7,326.30

Transfers_Of_Financial_Assets_1

Transfers Of Financial Assets (Narrative) (Details) (USD $)

3 Months Ended

9 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Oct. 19, 2012

Mar. 15, 2010

Aug. 29, 2012

Columbia Gas Of Ohio Receivables Corporation [Member]

Columbia Gas Of Pennsylvania Receivables Corporation [Member]

NIPSCO Accounts Receivable Corporation [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Accounts Receivable Program [Member]

Columbia Gas Of Ohio Receivables Corporation [Member]

Columbia Gas Of Pennsylvania Receivables Corporation [Member]

NIPSCO Accounts Receivable Corporation [Member]

Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

Accounts receivable securitization facility borrowings

$208.30

'

$208.30

'

$233.30

'

'

'

$515

'

'

'

Trade receivables, seasonal program maximum

'

'

'

'

'

'

'

'

'

240

75

200

Net receivables transferred

208.3

'

208.3

'

233.3

73.3

10

125

'

'

'

'

Securitization transaction fees

$0.50

$0.50

$2

$2.50

'

'

'

'

'

'

'

'

Transfers_Of_Financial_Assets_2

Transfers Of Financial Assets (Schedule Of Gross And Net Receivables Transferred As Well As Short-Term Borrowings Related To The Securitization Transactions) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Gross Receivables interest	$350.80	$525.30
Less: Receivables not transferred	142.5	292
Net receivables transferred	208.3	233.3
Accounts receivable securitization facility borrowings	$208.30	$233.30

Goodwill_Assets_Details

Goodwill Assets (Details) (USD $)	Sep. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Goodwill And Other Intangible Assets [Line Items]	'	'	'
Goodwill	$3,666.20	'	$3,677.30
Disposal Group, Including Discontinued Operation, Goodwill	'	11	'
Northern Indiana Gas Distribution [Member]	'	'	'
Goodwill And Other Intangible Assets [Line Items]	'	'	'
Goodwill	17.8	'	'
Disposal Group, Including Discontinued Operation, Goodwill	'	1	'
Columbia Gas Transmission Operations [Member]	'	'	'
Goodwill And Other Intangible Assets [Line Items]	'	'	'
Goodwill	2,000	'	'
Columbia Distribution [Member]	'	'	'
Goodwill And Other Intangible Assets [Line Items]	'	'	'
Goodwill	1,700	'	'
Disposal Group, Including Discontinued Operation, Goodwill	'	$10	'

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Jul. 24, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Apr. 30, 2013	Mar. 31, 2013
Income Taxes [Line Items]	'	'	'	'	'	'	'
Effective income tax rates	'	36.00%	35.70%	34.70%	34.80%	'	'
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate	'	'	'	35.00%	'	'	'
Income Taxes Receivable	'	'	'	'	'	'	$15.90
Operating Loss Carryforwards	'	'	'	'	'	'	0.6
Income tax refunds	'	'	'	'	'	70.6	75.1
Valuation Allowance, Deferred Tax Asset, Change in Amount	$3.20	'	'	'	'	'	'
Columbia Of Massachusetts [Member] | Previous [Member]	'	'	'	'	'	'	'
Income Taxes [Line Items]	'	'	'	'	'	'	'
Franchise Tax Rate	6.50%	'	'	'	'	'	'
Columbia Of Massachusetts [Member] | Future Date [Member]	'	'	'	'	'	'	'
Income Taxes [Line Items]	'	'	'	'	'	'	'
Franchise Tax Rate	8.00%	'	'	'	'	'	'

Pension_And_Other_Postretireme2

Pension And Other Postretirement Benefits (Narrative) (Details) (USD $)

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

3 Months Ended

9 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

31-May-13

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Aug. 31, 2013

Feb. 28, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Pension Plan [Member]

Pension Plan [Member]

Pension Plan [Member]

Pension Plan [Member]

Pension Plan [Member]

Pension Plan [Member]

Pension Plan [Member]

Pension Plan [Member]

Other Postretirement Benefits [Member]

Other Postretirement Benefits [Member]

Other Postretirement Benefits [Member]

Other Postretirement Benefits [Member]

Defined Benefit Plan Disclosure [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Pension and other postretirement benefit cost capitalized

$4.40

$8.20

$30.20

$19.10

'

'

'

'

'

'

'

'

'

'

'

'

'

Employer contributions

'

'

'

'

'

'

'

'

'

9.1

'

'

'

'

'

29.6

'

Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements

'

'

'

'

'

4

3.6

20.7

1.9

28.3

1.9

'

'

0

0

0

0

Change in Pension Projected Benefit Obligation, net of plan assets, due to Interim Measurement

'

'

'

'

30.7

'

'

'

'

'

'

1.7

18.6

'

'

'

'

Change in regulatory assets due to Interim Measurement

'

'

'

'

30.8

'

'

'

'

'

'

6.5

36.1

'

'

'

'

Change in Accumulated Other Comprehensive Income due to Interim Measurement

'

'

'

'

3.5

'

'

'

'

'

'

0.8

3.2

'

'

'

'

Change in Net Periodic Benefit Cost due to Interim Measurement

'

'

'

'

'

'

'

'

'

$3.60

'

'

'

'

'

'

'

Pension_And_Other_Postretireme3

Pension And Other Postretirement Benefits (Components Of The Plans' Net Periodic Benefits Cost) (Details) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension Plan [Member]	'	'	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'	'	'
Service Cost	$9	'	'	$9.40	$27.70	$28.20
Interest cost	24.9	'	'	28.2	73.5	84.6
Expected return on assets	-42	'	'	-41.2	-126.5	-123.4
Amortization of transition obligation	0	'	'	0	0	0
Amortization of prior service cost	0	'	'	0.1	0.2	0.3
Defined Benefit Plan, Amortization of Gains (Losses)	18.9	'	'	20.3	59.3	60.9
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements	4	3.6	20.7	1.9	28.3	1.9
Total Net Periodic Benefits Cost	14.8	'	'	18.7	62.5	52.5
Other Postretirement Benefits [Member]	'	'	'	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'	'	'	'
Service Cost	3	'	'	2.8	9	8.4
Interest cost	8	'	'	9.6	24.2	28.2
Expected return on assets	-7.6	'	'	-6.7	-22.8	-20.1
Amortization of transition obligation	0.2	'	'	0.3	0.4	0.9
Amortization of prior service cost	-0.2	'	'	0.5	-0.6	0.3
Defined Benefit Plan, Amortization of Gains (Losses)	2.8	'	'	2.3	8.4	7.1
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements	0	'	'	0	0	0
Total Net Periodic Benefits Cost	$6.20	'	'	$8.80	$18.60	$24.80

Pension_And_Other_Postretireme4

Pension And Other Postretirement Benefits Pension and Other Postretirement Benefits - Assumpted Used Table (Details) (Pension Plan [Member])	2 Months Ended	5 Months Ended	8 Months Ended	12 Months Ended
	Feb. 28, 2013	31-May-13	Aug. 31, 2013	Dec. 31, 2012
Pension Plan [Member]	'	'	'	'
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]	'	'	'	'
Discount Rate	3.50%	3.75%	4.25%	3.63%
Defined Benefit Plan, Expected Return on Plan Assets	8.30%	8.30%	8.30%	8.30%

Variable_Interests_and_Variabl1

Variable Interests and Variable Interest Entities (Narrative) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Schedule of Equity Method Investments [Line Items]	'	'
Payments made to Pure Air	$17.10	$16.50

LongTerm_Debt_Narrative_Detail

Long-Term Debt (Narrative) (Details) (USD $)	Jun. 03, 2013	Aug. 19, 2013	Jul. 22, 2013	Jul. 08, 2013	Apr. 12, 2013	Mar. 01, 2013	Apr. 15, 2013	Apr. 05, 2012	Oct. 10, 2013	Apr. 05, 2012	Apr. 15, 2013
In Millions, unless otherwise specified	Northern Indiana [Member]	Northern Indiana [Member]	Northern Indiana [Member]	Northern Indiana [Member]	NiSource Finance [Member]	NiSource Finance [Member]	NiSource Finance [Member]	NiSource Finance [Member]	NiSource Finance [Member]	NiSource Finance [Member]	NiSource Finance [Member]
	Pollution Control Bond [Member]	Medium-term Notes [Member]	Medium-term Notes [Member]	Medium-term Notes [Member]	4.80% Senior Unsecured Notes Due February 15, 2044 [Member]	6.15% Notes Due 2013 [Member]	LIBOR plus 125 basis points three-year bank term loan due April 15, 2016	LIBOR plus 125 basis points three-year bank term loan due April 15, 2016	5.65% Senior Unsecured Notes Due February 1, 2045	Previous Maximum [Member]	Current Maximum [Member]
										LIBOR plus 125 basis points three-year bank term loan due April 15, 2016	LIBOR plus 125 basis points three-year bank term loan due April 15, 2016
Debt Instrument [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Face amount of notes	$18	$30	$5	$15	$750	'	'	'	$500	$250	$325
Debt instrument maturity date	'	'	'	'	15-Feb-44	'	15-Apr-16	3-Apr-15	1-Feb-45	'	'
Repayments of Senior Debt	'	'	'	'	'	$420.30	'	'	'	'	'
Interest rate on debt	5.20%	7.16%	7.21%	7.35%	4.80%	6.15%	'	'	5.65%	'	'
Debt Instrument, Basis Spread on Variable Rate	'	'	'	'	'	'	1.25%	'	'	'	'
Long term debt note term	'	'	'	'	'	'	'3 years	'	'	'	'

ShortTerm_Borrowings_Narrative

Short-Term Borrowings (Narrative) (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	31-May-12	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012	Jun. 30, 2011	Feb. 15, 2013
				Revolving Credit Facility [Member]	Commercial Paper [Member]	Standby Letters of Credit [Member]	Standby Letters of Credit [Member]	Previous Maximum [Member]	Current Maximum [Member]
								Commercial Paper [Member]	Commercial Paper [Member]
Short-term Debt [Line Items]	'	'	'	'	'	'	'	'	'
Commercial paper outstanding	$612.50	$499.60	'	'	$612.50	'	'	'	'
Letters of Credit Outstanding, Amount	39.2	36.4	'	'	'	'	'	'	'
Revolving credit facility	'	'	2,000	2,000	1,500	'	'	500	1,500
Revolving Credit Facility, Expiration Date	28-Sep-18	'	'	'	'	'	'	'	'
Line of Credit Facility, Amount Outstanding	0	44	'	0	'	21.3	18.3	'	'
Accounts receivable securitization facility borrowings	208.3	233.3	'	'	'	'	'	'	'
Short-term borrowings	$820.80	$776.90	'	'	'	'	'	'	'

ShortTerm_Borrowings_Schedule_

Short-Term Borrowings (Schedule Of Short-Term Borrowings) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Short-term Debt [Line Items]	'	'
Commercial paper	$612.50	$499.60
Credit facilities borrowings	0	44
Accounts receivable securitization facility borrowings	208.3	233.3
Total short-term borrowings	820.8	776.9
Letters of Credit Outstanding, Amount	39.2	36.4
Commercial Paper [Member]	'	'
Short-term Debt [Line Items]	'	'
Commercial paper	$612.50	'
Commercial Paper/credit facilities borrowings, weighted average interest rate	0.67%	1.11%
Credit Facilities [Member]	'	'
Short-term Debt [Line Items]	'	'
Commercial Paper/credit facilities borrowings, weighted average interest rate	0.00%	3.73%

ShareBased_Compensation_Narrat

Share-Based Compensation (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	11-May-10
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	'	'	'	'	8,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	6,734,008	'	6,734,008	'	'
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	$3.20	$2.20	$6.10	$5	'
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	21.8	'	21.8	'	'
Employee Service Share Based Compensation Nonvested Awards Weighted Average Remaining Requisite Service Period	'	'	'2 years	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	500,000	'	500,000	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$22.44	'	$22.44	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	'	'	0	0	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	4.5	'	4.5	'	'
Employee Service Share-based Compensation, Cash Received from Exercise of Stock Options	'	'	22.6	24.7	'
Defined Contribution Plan, Cost Recognized	7.9	6.7	22.2	19.4	'
Allocated Share-based Compensation Expense	8.8	6.3	17.5	13.6	'
Restricted Awards [Member]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	'	'	69,651	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	'	'	1.8	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	371,870	'	371,870	'	'
Performance Shares [Member]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	'	'	664,776	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	'	'	$15.70	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	1,974,337	'	1,974,337	'	'
Omnibus Plan [Member] | Restricted Awards [Member]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued	'	'	148,702	'	'
Director Plan [Member] | Restricted Awards [Member]	'	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'
Share-based Goods and Nonemployee Services Transaction, Quantity of Securities Issued	'	'	181,106	'	'

Other_Commitments_And_Continge2

Other Commitments And Contingencies (Narrative) (Details) (USD $)

9 Months Ended

12 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Sep. 30, 2013

Dec. 31, 2012

31-May-12

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2013

MGP Sites

MGP Sites

Columbia Transmission [Member]

Columbia Transmission [Member]

Millennium Pipeline Company, L.L.C [Member]

Guarantees Of Subsidiaries Debt [Member]

Guarantees Supporting Energy Commodity Transactions Of Subsidiaries [Member]

Letters Of Credit [Member]

Other Guarantees [Member]

Commercial Paper [Member]

Accounts Receivable Securitization [Member]

Maximum [Member]

Revolving Credit Facility [Member]

Commercial Paper [Member]

Northern Indiana [Member]

Other Commitments And Contingencies [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Guarantees

$8,213.50

'

'

'

'

'

'

$16.20

$7,210.50

$10.70

$39.20

$132.30

$612.50

$208.30

'

'

'

Revolving credit facility, maximum

'

'

2,000

'

'

'

'

'

'

'

'

'

'

'

'

2,000

1,500

Line of Credit Facility, Expiration Date

28-Sep-18

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Line of Credit Facility, Amount Outstanding

0

44

'

'

'

'

'

'

'

'

'

'

'

'

'

0

'

Commercial paper

612.5

499.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

612.5

Accounts receivable securitization facility borrowings

208.3

233.3

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Additional purchase and sales agreement guarantees

28

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of interest in Millennium

47.50%

'

'

'

'

'

'

47.50%

'

'

'

'

'

'

'

'

'

Fair value of guarantee obligations

'

'

'

'

'

'

'

1.5

'

'

'

'

'

'

'

'

'

Gain (Loss) Related to Litigation Settlement

17.5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Recorded reserves to cover environmental remediation at various sites

149.5

160.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Payments for capital improvements

'

'

'

'

'

'

'

'

'

'

'

'

'

'

860

'

'

Remaining Payments for Capital Improvements

'

'

'

'

'

25.6

'

'

'

'

'

'

'

'

350

'

'

Number of waste disposal sites identified by program

'

'

'

67

'

'

'

'

'

'

'

'

'

'

'

'

'

Original number of facilities AOC covered under conduct characterization and remediation activities, approximately

'

'

'

'

'

'

245

'

'

'

'

'

'

'

'

'

'

Number of liquid removal points AOC covered under conduct characterization and remediation activities

'

'

'

'

'

'

13,000

'

'

'

'

'

'

'

'

'

'

Number of mercury measurement stations AOC covered under conduct characterization and remediation activities

'

'

'

'

'

'

2,200

'

'

'

'

'

'

'

'

'

'

Number of storage well locations AOC covered under conduct characterization and remediation activities

'

'

'

'

'

'

3,700

'

'

'

'

'

'

'

'

'

'

Proposed penalty of NOV asserts violations of Pennsylvania Clean Streams law and Pennsylvania Solid Waste Management act

'

'

'

'

'

'

1

'

'

'

'

'

'

'

'

'

'

Liability for estimated remediation costs

'

'

'

131.4

132.6

21.7

11.8

'

'

'

'

'

'

'

'

'

'

Reasonably possible remediation costs variance from reserve

'

'

'

$25

'

'

'

'

'

'

'

'

'

'

'

'

'

Remaining number of facilities AOC covered under conduct characterization and remediation activities, approximately

'

'

'

'

'

'

50

'

'

'

'

'

'

'

'

'

'

Sites Associated With Former Propane Operations

4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Sites Associated With Former Petroleum Operations

10

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Other_Commitments_And_Continge3

Other Commitments And Contingencies (Existence And Expiration Of Commercial Commitments) (Details) (USD $)	Sep. 30, 2013
In Millions, unless otherwise specified
Other Commitments And Contingencies [Line Items]	'
2013	$850.30
2014	570.7
2015	249.2
2016	616.5
2017	507
After	5,419.80
Total	8,213.50
Guarantees Of Subsidiaries Debt [Member]	'
Other Commitments And Contingencies [Line Items]	'
2013	0
2014	500
2015	230
2016	616.5
2017	507
After	5,357
Total	7,210.50
Guarantees Supporting Energy Commodity Transactions Of Subsidiaries [Member]	'
Other Commitments And Contingencies [Line Items]	'
2013	10.7
2014	0
2015	0
2016	0
2017	0
After	0
Total	10.7
Accounts Receivable Securitization [Member]	'
Other Commitments And Contingencies [Line Items]	'
2013	208.3
2014	0
2015	0
2016	0
2017	0
After	0
Total	208.3
Lines Of Credit [Member]	'
Other Commitments And Contingencies [Line Items]	'
2013	612.5
2014	0
2015	0
2016	0
2017	0
After	0
Total	612.5
Letters Of Credit [Member]	'
Other Commitments And Contingencies [Line Items]	'
2013	0.7
2014	22.3
2015	16.2
2016	0
2017	0
After	0
Total	39.2
Other Guarantees [Member]	'
Other Commitments And Contingencies [Line Items]	'
2013	18.1
2014	48.4
2015	3
2016	0
2017	0
After	62.8
Total	$132.30

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Loss (Narrative) (Details) (Millennium Pipeline Company, L.L.C [Member], USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Millennium Pipeline Company, L.L.C [Member]	'	'
Accumulated Other Comprehensive Loss [Line Items]	'	'
Other Comprehensive Income Unrecognized Gain Loss On Derivatives Arising During Period Net Of Tax	$17.90	$18.70
Debt instrument maturity date	1-Jun-25	'

Accumulated_Other_Comprehensiv3

Accumulated Other Comprehensive Loss (Components Of Accumulated Other Comprehensive Loss) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning Balance	($62)	'	($65.50)	'
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0.3	'	0.6	'
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	1.3	'	4.5	'
Other Comprehensive Income (Loss), Net of Tax	1.6	2.2	5.1	2.9
Ending Balance	-60.4	'	-60.4	'
Accumulated Net Unrealized Investment Gain (Loss) [Member]	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning Balance	-0.7	'	2.6	'
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	1	'	-1.9	'
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	-0.1	'	-0.5	'
Other Comprehensive Income (Loss), Net of Tax	0.9	'	-2.4	'
Ending Balance	0.2	'	0.2	'
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning Balance	-27.2	'	-28.6	'
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	-0.1	'	-0.1	'
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0.7	'	2.1	'
Other Comprehensive Income (Loss), Net of Tax	0.6	'	2	'
Ending Balance	-26.6	'	-26.6	'
Accumulated Defined Benefit Plans Adjustment [Member]	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning Balance	-34.1	'	-39.5	'
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	-0.6	'	2.6	'
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0.7	'	2.9	'
Other Comprehensive Income (Loss), Net of Tax	0.1	'	5.5	'
Ending Balance	($34)	'	($34)	'

Business_Segment_Information_N

Business Segment Information (Narrative) (Details)	9 Months Ended
	Sep. 30, 2013
Segment Reporting [Abstract]	'
Primary business segments	'3
Number of counties in which electric service provided by Electric Operations	20

Business_Segment_Information_S

Business Segment Information (Schedule Of Operating Income Derived From Revenues And Expenses By Segment) (Details) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	$1,076.80	$956.20	$4,060.50	$3,637.30
Consolidated Operating Income (Loss)	176.4	131.5	799.3	733.5
Gas Distribution Operations [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	409.5	379	2,127	1,883.20
Consolidated Operating Income (Loss)	-5	10.4	279.1	263.4
Gas Distribution Operations [Member] | Unaffiliated [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	409.5	378.9	2,126.80	1,882.80
Gas Distribution Operations [Member] | Intersegment [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	0	0.1	0.2	0.4
Columbia Pipeline Group Operations [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	282.7	188.1	857.9	704.5
Consolidated Operating Income (Loss)	98.7	38.8	321	268.9
Columbia Pipeline Group Operations [Member] | Unaffiliated [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	251.3	156.6	752	599.1
Columbia Pipeline Group Operations [Member] | Intersegment [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	31.4	31.5	105.9	105.4
Electric Operations [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	413.7	418.5	1,176.40	1,149
Consolidated Operating Income (Loss)	87.5	83.7	212.2	200.2
Electric Operations [Member] | Unaffiliated [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	413.6	418.3	1,175.90	1,148.40
Electric Operations [Member] | Intersegment [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	0.1	0.2	0.5	0.6
Corporate and Other [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	122	121.7	357.1	352.3
Consolidated Operating Income (Loss)	-4.8	-1.4	-13	1
Corporate and Other [Member] | Unaffiliated [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	2.4	2.4	5.8	7
Corporate and Other [Member] | Intersegment [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	119.6	119.3	351.3	345.3
Eliminations [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Revenues	($151.10)	($151.10)	($457.90)	($451.70)

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information (Details) (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Supplemental Cash Flow [Line Items]	'	'
Capital expenditures included in current liabilities	$202.70	$119.60
Stock issuance to employee savings plans	22.2	19.4
Cash paid for interest, net of interest capitalized amounts	359.4	336.1
Cash paid for income taxes	$8.50	$8.40