COMMON EQUITY - CAPITAL TRANSACTIONS WITH SUBSIDIARIES (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014
Capital Transactions with Subsidiaries
Dividends to parent	$ 92.7
Return of capital to parent	52.5
Equity contributions from parent	108.6
WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	86.51%
IBS
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	0
Equity contributions from parent	25.0
ITF
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	0
Equity contributions from parent	33.4
MERC
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	27.0
Equity contributions from parent	0
MGU
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	13.0
Equity contributions from parent	0
UPPCO
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	12.5
Equity contributions from parent	0
UPPCO | WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	2.37%
WPS
Capital Transactions with Subsidiaries
Dividends to parent	55.9
Return of capital to parent	0
Equity contributions from parent	40.0
WPS | WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	11.12%
WPS Investments, LLC
Capital Transactions with Subsidiaries
Dividends to parent	36.8
Return of capital to parent	0
Equity contributions from parent	$ 10.2