COMMON EQUITY (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Capital Transactions with Subsidiaries
Dividends To Parent	$ 44.4
Return Of Capital To Parent	21.0
Equity Contributions From Parent	213.4
WPS
Capital Transactions with Subsidiaries
Dividends To Parent	27.1
Equity Contributions From Parent	200.0
WPS | WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	11.66%
WPS Investments, LLC
Capital Transactions with Subsidiaries
Dividends To Parent	17.3
Equity Contributions From Parent	1.7
Ownership interest (as a percent)	85.86%
MERC
Capital Transactions with Subsidiaries
Return Of Capital To Parent	21.0
UPPCO | WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	2.48%
ITF
Capital Transactions with Subsidiaries
Equity Contributions From Parent	$ 11.7