v2.3.0.11

Business Segment Information (Narrative) (Details)	6 Months Ended
	Jun. 30, 2011
Business Segment Information
Primary business segments	3
Number of counties in which electric service provided by Electric Operations	20

X

- Definition

Primary Business Segments

+ Details

Name:	ni_PrimaryBusinessSegments
Namespace Prefix:	ni
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Service Area By County

+ Details

Name:	ni_ServiceAreaByCounty
Namespace Prefix:	ni
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_SegmentReportingAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration