SHORT-TERM DEBT AND LINES OF CREDIT (Details 2) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Short-term borrowings
Total short-term credit capacity	$ 1,610.0	$ 1,610.0
Letters of credit issued inside credit facilities	52.4	25.5
Short-term borrowings outstanding	326.0	482.4
Available capacity under existing agreements	1,231.6	1,102.1
Maximum
Short-term borrowings
Debt to capitalization ratio required to be maintained (as a percent)	65.00%
Integrys Energy Group, Inc.
Short-term borrowings
Short-term borrowings outstanding	123.2	208.4
Integrys Energy Group, Inc. | Maximum
Short-term borrowings
Debt to capitalization ratio required to be maintained (as a percent)	65.00%
WPS | Maximum
Short-term borrowings
Debt to capitalization ratio required to be maintained (as a percent)	65.00%
PGL | Maximum
Short-term borrowings
Debt to capitalization ratio required to be maintained (as a percent)	65.00%
Revolving credit facility maturing on May 17, 2014 | Integrys Energy Group, Inc.
Short-term borrowings
Total short-term credit capacity	275.0	275.0
Revolving credit facility maturing on May 17, 2014 | WPS
Short-term borrowings
Total short-term credit capacity	135.0	135.0
Revolving credit facility maturing on May 17, 2016 | Integrys Energy Group, Inc.
Short-term borrowings
Total short-term credit capacity	200.0	200.0
Revolving credit facility maturing on June 13, 2017 | Integrys Energy Group, Inc.
Short-term borrowings
Total short-term credit capacity	635.0	635.0
Revolving credit facility maturing on June 13, 2017 | WPS
Short-term borrowings
Total short-term credit capacity	115.0	115.0
Revolving credit facility maturing on June 13, 2017 | PGL
Short-term borrowings
Total short-term credit capacity	250.0	250.0
Commercial paper
Short-term borrowings
Short-term borrowings outstanding	$ 326.0	$ 482.4	$ 303.3