RELATED PARTY TRANSACTIONS (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Related Party Transactions
Long-term debt to parent	$ 3.8		$ 6.3
Current portion of long-term debt to parent	2.3		0
Earnings from equity method investments	2.8	3.0
ATC
Related Party Transactions
Accounts payable to related parties	12.6		10.4
Charges from equity method investee for network transmission services	24.7	24.6
Charges to equity method investee for services and/or construction	2.4	1.8
WRPC
Related Party Transactions
Purchases from related party	1.0	1.0
Charges to equity method investee for services and/or construction	0.4	0.2
WPS Investments, LLC
Related Party Transactions
Earnings from equity method investments	2.5	2.5
Equity method investment, ownership interest (as a percent)	11.24%
Integrys Energy Group
Related Party Transactions
Liability related to income tax allocation	6.5		6.7
UPPCO | Electric Utility
Related Party Transactions
Sales to related party	5.4	5.3
Integrys Energy Services | Natural gas transactions
Related Party Transactions
Sales to related party	0.1	0.1
Purchases from related party	2.3	0.2
WPS Leasing | Integrys Energy Group
Related Party Transactions
Long-term debt to parent	6.1		6.3
Interest expense	$ 0.1	$ 0.2