v2.3.0.11

Variable Interests and Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011
Variable Interests and Variable Interest Entities
Ownership percentage in housing real estate Investment	99.00%
Variable Interest Entity, net investment	$ 1.2
Variable Interest Entity, gross assets	28.9
Variable Interest Entity, current assets	1.2
Variable Interest Entity, non current assets	27.7
Variable Interest Entity, long term debt	11.3
Variable Interest Entity, assets restricted to settle the obligations of the entity	$ 0.7
Variable Interest Entity, contract period	20 Years

X

- Definition

Variable interest, assets restricted to settle the obligations of the entity.

+ Details

Name:	ni_VariableInterestAssetsRestrictedToSettleObligationsOfEntity
Namespace Prefix:	ni
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Variable interest carrying amount, current assets.

+ Details

Name:	ni_VariableInterestCarryingAmountCurrentAssets
Namespace Prefix:	ni
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Variable interest carrying amount long term debt.

+ Details

Name:	ni_VariableInterestCarryingAmountLongTermDebt
Namespace Prefix:	ni
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Variable interest carrying amount noncurrent assets.

+ Details

Name:	ni_VariableInterestCarryingAmountNoncurrentAssets
Namespace Prefix:	ni
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Variable interest, Contract period.

+ Details

Name:	ni_VariableInterestContractPeriod
Namespace Prefix:	ni
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Variable Interest Entities and Equity Investments.

+ Details

Name:	ni_VariableInterestEntitiesAndEquityInvestmentsAbstract
Namespace Prefix:	ni
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Variable Interest Net Investment In Entity

+ Details

Name:	ni_VariableInterestNetInvestmentInEntity
Namespace Prefix:	ni
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=6970148&loc=d3e5710-111685

+ Details

Name:	us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Percentage of the Variable Interest Entity's (VIE) voting interest owned by (or beneficial interest in) the reporting entity (directly or indirectly).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6970148&loc=SL6759159-111685

+ Details

Name:	us-gaap_VariableInterestEntityOwnershipPercentage
Namespace Prefix:	us-gaap
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration