SCHEDULE I - CONDENSED PARENT COMPANY FINANCIAL STATEMENTS STATEMENTS OF COMPREHENSIVE INCOME (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Net income (loss) attributed to common shareholders	$ 131.6	$ 38.1	$ (5.4)	$ 187.5	$ 68.0	$ 65.7	$ 48.8	$ 98.9	$ 351.8	$ 281.4	$ 227.4
Cash flow hedges
Unrealized net gains (losses) arising during period, net of tax of $ – million, $0.1 million, and $(0.3) million, respectively									0.7	(0.2)	1.5
Unrealized net gains (losses) arising during period, tax									0.1	(0.1)	0.4
Reclassification of net (gains) losses to net income, net of tax of $2.0 million, $(1.0) million, and $0.2 million, respectively									1.4	6.5	7.4
Reclassification of net losses to net income, tax									3.6	2.0	4.4
Cash flow hedges, net									2.1	6.3	8.9
Defined benefit plans
Pension and other postretirement benefit costs arising during the period, net of tax of $ - million, $(0.9) million, and $(0.7) million, respectively									13.2	(6.1)	(7.5)
Pension and other postretirement benefit costs arising during period, tax									8.9	(4.4)	(5.7)
Amortization of pension and other postretirement benefit costs included in net periodic benefit cost, net of tax of $0.9 million, $0.4 million, and $0.1 million, respectively									2.4	1.4	0.8
Amortization of pension and other postretirement benefit costs included in net periodic benefit cost, tax									1.7	1.0	0.6
Defined benefit plans, net									15.6	(4.7)	(6.7)
Other comprehensive income, net of tax									17.7	1.6	2.2
Comprehensive income attributed to common shareholders									369.5	283.0	229.6
Integrys Energy Group, Inc.
Condensed Financial Statements, Captions [Line Items]
Net income (loss) attributed to common shareholders									351.8	281.4	227.4
Cash flow hedges
Unrealized net gains (losses) arising during period, net of tax of $ – million, $0.1 million, and $(0.3) million, respectively									0.6	(0.1)	0.3
Unrealized net gains (losses) arising during period, tax									0	0.1	(0.3)
Reclassification of net (gains) losses to net income, net of tax of $2.0 million, $(1.0) million, and $0.2 million, respectively									(0.9)	2.1	1.1
Reclassification of net losses to net income, tax									2.0	(1.0)	0.2
Cash flow hedges, net									(0.3)	2.0	1.4
Defined benefit plans
Pension and other postretirement benefit costs arising during the period, net of tax of $ - million, $(0.9) million, and $(0.7) million, respectively									1.1	0.9	0
Pension and other postretirement benefit costs arising during period, tax									0	(0.9)	(0.7)
Amortization of pension and other postretirement benefit costs included in net periodic benefit cost, net of tax of $0.9 million, $0.4 million, and $0.1 million, respectively									(0.5)	(0.1)	0.2
Amortization of pension and other postretirement benefit costs included in net periodic benefit cost, tax									0.9	0.4	0.1
Defined benefit plans, net									0.6	0.8	0.2
Other comprehensive income (loss) from subsidiaries, net of tax									17.4	(1.2)	0.6
Other comprehensive income, net of tax									17.7	1.6	2.2
Comprehensive income attributed to common shareholders									$ 369.5	$ 283.0	$ 229.6