COMMON EQUITY - CAPITAL TRANSACTIONS WITH SUBSIDIARIES (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Capital Transactions with Subsidiaries
Dividends to parent	$ 139.1
Return of capital to parent	52.5
Equity contributions from parent	295.5
WPS Investments, LLC
Capital Transactions with Subsidiaries
Ownership interest (as a percent)	88.95%
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	45.5
MERC
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	27.0
Equity contributions from parent	12.0
MGU
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	13.0
Equity contributions from parent	0
PGL
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	0
Equity contributions from parent	65.0
UPPCO
Capital Transactions with Subsidiaries
Dividends to parent	0
Return of capital to parent	12.5
Equity contributions from parent	94.4
WPS
Capital Transactions with Subsidiaries
Dividends to parent	83.9
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)	11.05%
WPS Investments, LLC
Capital Transactions with Subsidiaries
Dividends to parent	55.2
Return of capital to parent	0
Equity contributions from parent	$ 13.6