PROPOSED MERGER WITH WISCONSIN ENERGY CORPORATION (Details) (USD $)	1 Months Ended
Jun. 30, 2014 customer
Business Combinations [Abstract]
Number of Wisconsin Energy Corporation shares received for each Integrys Energy Group share at closing	1.128
Cash per share of Integrys Energy Group common stock	$ 18.58
Integrys Energy Group shareholders ownership percentage of combined company	28.00%
Wisconsin Energy Corporation shareholders ownership percentage of combined company	72.00%
Number of total natural gas and electric customers upon closing of the merger	4,300,000

The cash to be received per share of Integrys Energy Group common stock owned under the merger agreement.

No definition available.

Name:	teg_CashpershareofIntegrysEnergyGroupcommonstock
Namespace Prefix:	teg_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Integrys Energy Group ownership percentage of combined company upon closing of the merger agreement.

+ References

No definition available.

+ Details

Name:	teg_IntegrysEnergyGroupshareholdersownershippercentageofcombinedcompany
Namespace Prefix:	teg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of total natural gas and electric customers across Wisconsin, Illinois, Michigan, and Minnesota upon closing of the merger agreement between Integrys Energy Group and Wisconsin Energy Corporation.

+ References

No definition available.

+ Details

Name:	teg_Numberoftotalnaturalgasandelectriccustomersuponclosingofthemerger
Namespace Prefix:	teg_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Wisconsin Energy Corporation shares to be received for each share of Integrys Energy Group under the merger agreement at the close of the transaction.

+ References

No definition available.

+ Details

Name:	teg_NumberofWisconsinEnergyCorporationsharesreceivedforeachIntegrysEnergyGroupshareatclosing
Namespace Prefix:	teg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Wisconsin Energy Corporation shareholders ownership percentage of combined company upon closing of the merger agreement.

+ References

No definition available.

+ Details

Name:	teg_WisconsinEnergyCorporationshareholdersownershippercentageofcombinedcompany
Namespace Prefix:	teg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_BusinessCombinationsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration