RELATED PARTY TRANSACTIONS (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
RELATED PARTY TRANSACTIONS
Long-term debt to parent	$ 2.9	$ 6.3
Current portion of long-term debt to parent	2.5	0
Equity earnings from WPS Investments, LLC	10.3	11.3	11.0
ATC
RELATED PARTY TRANSACTIONS
Accounts payable to related parties	8.2	10.4
Charges from equity method investee for network transmission services	99.0	98.4	94.2
Charges to equity method investee for services, construction, and operations	8.6	9.5	10.4
WRPC
RELATED PARTY TRANSACTIONS
Purchases from related party	3.7	3.7	5.0
Charges to equity method investee for services, construction, and operations	1.4	0.9	0.8
Net proceeds from WRPC sales of energy to MISO	0	0	2.9
WPS Investments, LLC
RELATED PARTY TRANSACTIONS
Equity earnings from WPS Investments, LLC	9.5	10.2	10.2
Equity method investment, ownership interest (as a percent)	10.98%
IBS
RELATED PARTY TRANSACTIONS
Number of categories of services provided by related party	15
Integrys Energy Group
RELATED PARTY TRANSACTIONS
Liability related to income tax allocation	6.1	6.7
UPPCO \| Electric Utility
RELATED PARTY TRANSACTIONS
Sales to related party	15.3	22.8	22.2
Integrys Transportation Fuels LLC \| Electric Utility
RELATED PARTY TRANSACTIONS
Sales to related party	0.1	0	0
Integrys Energy Services \| Natural gas transactions
RELATED PARTY TRANSACTIONS
Sales to related party	0.6	0.5	0.6
Purchases from related party	2.5	0.9	0.7
WPS Leasing \| Integrys Energy Group
RELATED PARTY TRANSACTIONS
Long-term debt to parent	5.4	6.3
Interest expense	$ 0.5	$ 0.5	$ 0.5

Amount for accounts payable to related parties.

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