MISCELLANEOUS INCOME (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Component of Other Income, Nonoperating [Line Items]
Total miscellaneous income	$ 29.8	$ 9.3	$ 5.3
Equity portion of AFUDC
Component of Other Income, Nonoperating [Line Items]
Total miscellaneous income	10.8	2.9	0.7
Seams elimination charge adjustment (SECA) settlement at Integrys Energy Services
Component of Other Income, Nonoperating [Line Items]
Total miscellaneous income	5.7	0	0
Federal excise tax credit
Component of Other Income, Nonoperating [Line Items]
Total miscellaneous income	4.1	0	0
Key executive life insurance income for retired employees
Component of Other Income, Nonoperating [Line Items]
Total miscellaneous income	2.2	2.6	2.3
Gains (losses) on exchange-traded funds held at IBS
Component of Other Income, Nonoperating [Line Items]
Total miscellaneous income	2.2	1.3	(0.1)
Other
Component of Other Income, Nonoperating [Line Items]
Total miscellaneous income	$ 4.8	$ 2.5	$ 2.4