COMMON EQUITY - CAPITAL TRANSACTIONS WITH SUBSIDIARIES (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Capital Transactions with Subsidiaries
Dividends to parent	$ 46.3
Return of capital to parent	28.5
Equity contributions from parent	37.5
WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	86.37%
IBS
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	0
Equity contributions from parent	15.0
ITF
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	0
Equity contributions from parent	17.4
MERC
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	18.0
Equity contributions from parent	0
MGU
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	7.0
Equity contributions from parent	0
UPPCO
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	3.5
Equity contributions from parent	0
UPPCO | WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	2.39%
WPS
Capital Transactions with Subsidiaries
Dividends to parent	28.0
Return of capital to parent	0
Equity contributions from parent	0
WPS | WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	11.24%
WPS Investments, LLC
Capital Transactions with Subsidiaries
Dividends to parent	18.3
Return of capital to parent	0
Equity contributions from parent	$ 5.1