INVENTORIES (Details) (PGL and NSG, USD $) In Millions, unless otherwise specified	Mar. 31, 2015
PGL and NSG
Inventories
Temporary LIFO liquidation credit	$ 33.5

Represents the difference between current projected replacement cost and the LIFO cost for quantities of natural gas temporarily withdrawn from storage.

No definition available.

Name:	teg_TemporaryLIFOLiquidationCredit
Namespace Prefix:	teg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant