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Segment Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2013 mi Entity Segment
Segment Reporting Information [Line Items]
No of segments	4
No of subsidiaries	3
Length Of Pipeline	86
Granite State Gas Transmission Inc
Segment Reporting Information [Line Items]
Length Of Pipeline	86
No of major pipeline	3

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- Details

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- Definition

Length Of Pipeline

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- Definition

Number of Interconnected Interstate Pipelines

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- Definition

Number Of Segments

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- Definition

Number of Subsidiaries

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