INVENTORIES (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Temporary LIFO liquidation credit [Line Items]
Temporary LIFO liquidation credit	$ 150.9	$ 0
PGL and NSG
Temporary LIFO liquidation credit [Line Items]
Temporary LIFO liquidation credit	$ 150.9

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the difference between current projected replacement cost and the LIFO cost for quantities of natural gas temporarily withdrawn from storage.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