SCHEDULE I - CONDENSED PARENT COMPANY FINANCIAL STATEMENTS STATEMENTS OF COMPREHENSIVE INCOME (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net income attributed to common shareholders	$ 276.9	$ 351.8	$ 281.4
Cash flow hedges
Unrealized net gains (losses) arising during period, net of tax of $ - million, $ - million, and $0.1 million, respectively	0	0.7	(0.2)
Reclassification of net (gains) losses to net income, net of tax of $1.2 million, $2.0 million, and $(1.0) million, respectively	(0.1)	1.4	6.5
Reclassification of net (gains) losses to net income, tax	1.2	3.6	2.0
Cash flow hedges, net	(0.1)	2.1	6.3
Defined benefit plans
Pension and other postretirement benefit adjustments arising during period, net of tax of $(5.5) million, $ - million, and $(0.9) million, respectively	(6.0)	13.2	(6.1)
Pension and other postretirement benefit adjustments arising during period, tax	(3.0)	8.9	(4.4)
Amortization of pension and other postretirement benefit costs included in net periodic benefit cost, net of tax of $0.2 million, $0.9 million, and $0.4 million, respectively	1.7	2.4	1.4
Amortization of pension and other postretirement benefit costs included in net periodic benefit cost, tax	0.8	1.7	1.0
Defined benefit plans, net	(4.3)	15.6	(4.7)
Other comprehensive income (loss), net of tax	(4.4)	17.7	1.6
Comprehensive income attributed to common shareholders	272.5	369.5	283.0
Integrys Energy Group, Inc.
Condensed Financial Statements, Captions [Line Items]
Net income attributed to common shareholders	276.9	351.8	281.4
Cash flow hedges
Unrealized net gains (losses) arising during period, net of tax of $ - million, $ - million, and $0.1 million, respectively	0	0.6	(0.1)
Unrealized net gains (losses) arising during period, tax	0	0	0.1
Reclassification of net (gains) losses to net income, net of tax of $1.2 million, $2.0 million, and $(1.0) million, respectively	(0.1)	(0.9)	2.1
Reclassification of net (gains) losses to net income, tax	1.2	2.0	(1.0)
Cash flow hedges, net	(0.1)	(0.3)	2.0
Defined benefit plans
Pension and other postretirement benefit adjustments arising during period, net of tax of $(5.5) million, $ - million, and $(0.9) million, respectively	(9.6)	1.1	0.9
Pension and other postretirement benefit adjustments arising during period, tax	(5.5)	0	(0.9)
Amortization of pension and other postretirement benefit costs included in net periodic benefit cost, net of tax of $0.2 million, $0.9 million, and $0.4 million, respectively	0.3	(0.5)	(0.1)
Amortization of pension and other postretirement benefit costs included in net periodic benefit cost, tax	0.2	0.9	0.4
Defined benefit plans, net	(9.3)	0.6	0.8
Other comprehensive income (loss) from subsidiaries, net of tax	5.0	17.4	(1.2)
Other comprehensive income (loss), net of tax	(4.4)	17.7	1.6
Comprehensive income attributed to common shareholders	$ 272.5	$ 369.5	$ 283.0