COMMON EQUITY (Details 4) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Capital Transactions with Subsidiaries
Dividends to parent	$ 89.2
Return of capital to parent	74.0
Equity contributions from parent	224.5
WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	86.02%
ITF
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	0
Equity contributions from parent	17.7
MERC
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	21.0
Equity contributions from parent	0
MGU
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	12.5
Equity contributions from parent	0
UPPCO
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	5.5
Equity contributions from parent	0
UPPCO | WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	2.45%
WPS
Capital Transactions with Subsidiaries
Dividends to parent	54.3
Return of capital to parent	35.0
Equity contributions from parent	200.0
WPS | WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	11.53%
WPS Investments, LLC
Capital Transactions with Subsidiaries
Dividends to parent	34.9
Return of capital to parent	0
Equity contributions from parent	$ 6.8