SCHEDULE I - CONDENSED PARENT COMPANY FINANCIAL STATEMENTS STATEMENTS OF INCOME (Details) (USD $) In Millions, except Per Share data, 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]
Operating income	$ 226.2	$ 55.3	$ (6.9)	$ 293.1	$ 118.8	$ 108.5	$ 87.1	$ 153.1	$ 567.7	$ 467.5	$ 406.8
Equity earnings from subsidiaries									91.5	87.2	79.4
Miscellaneous income									29.8	9.3	5.3
Interest expense									128.2	120.2	128.2
Other expense									(6.9)	(23.7)	(43.5)
Income before taxes									560.8	443.8	363.3
Provision for income taxes									210.8	149.8	133.3
Net income from continuing operations	132.3	39.4	(3.9)	182.2	69.2	74.3	51.7	98.8	350.0	294.0	230.0
Net income 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
Average shares of common stock
Basic (in shares)									79.5	78.6	78.6
Diluted (in shares)									80.1	79.3	79.1
Earnings (loss) per common share (basic)
Net income from continuing operations (in dollars per share)	$ 1.64	$ 0.49	$ (0.06)	$ 2.30	$ 0.87	$ 0.94	$ 0.65	$ 1.25	$ 4.37	$ 3.70	$ 2.89
Discontinued operations, net of tax (in dollars per share)	$ 0.00	$ (0.01)	$ (0.01)	$ 0.08	$ 0.00	$ (0.10)	$ (0.03)	$ 0.01	$ 0.06	$ (0.12)	$ 0.00
Earnings per common share (basic) (in dollars per share)	$ 1.64	$ 0.48	$ (0.07)	$ 2.38	$ 0.87	$ 0.84	$ 0.62	$ 1.26	$ 4.43	$ 3.58	$ 2.89
Earnings (loss) per common share (diluted)
Net income from continuing operations (in dollars per share)	$ 1.63	$ 0.48	$ (0.06)	$ 2.29	$ 0.86	$ 0.93	$ 0.65	$ 1.24	$ 4.33	$ 3.67	$ 2.87
Discontinued operations, net of tax (in dollars per share)	$ 0.00	$ (0.01)	$ (0.01)	$ 0.08	$ 0.00	$ (0.10)	$ (0.03)	$ 0.01	$ 0.06	$ (0.12)	$ 0.00
Earnings per common share (diluted) (in dollars per share)	$ 1.63	$ 0.47	$ (0.07)	$ 2.37	$ 0.86	$ 0.83	$ 0.62	$ 1.25	$ 4.39	$ 3.55	$ 2.87
Integrys Energy Group, Inc.
Condensed Financial Statements, Captions [Line Items]
Operating expense									8.2	6.0	5.9
Operating income									(8.2)	(6.0)	(5.9)
Equity earnings from subsidiaries									397.1	332.4	275.5
Miscellaneous income									18.5	21.2	24.2
Interest expense									52.1	50.0	52.2
Other expense									363.5	303.6	247.5
Income before taxes									355.3	297.6	241.6
Provision for income taxes									8.3	6.5	14.7
Net income from continuing operations									347.0	291.1	226.9
Discontinued operations from Parent Company, net of tax									0.6	1.4	(0.2)
Discontinued operations from subsidiaries, net of tax									4.2	(11.1)	0.7
Net income attributed to common shareholders									$ 351.8	$ 281.4	$ 227.4
Average shares of common stock
Basic (in shares)									79.5	78.6	78.6
Diluted (in shares)									80.1	79.3	79.1
Earnings (loss) per common share (basic)
Net income from continuing operations (in dollars per share)									$ 4.37	$ 3.70	$ 2.89
Discontinued operations, net of tax (in dollars per share)									$ 0.06	$ (0.12)	$ 0.00
Earnings per common share (basic) (in dollars per share)									$ 4.43	$ 3.58	$ 2.89
Earnings (loss) per common share (diluted)
Net income from continuing operations (in dollars per share)									$ 4.33	$ 3.67	$ 2.87
Discontinued operations, net of tax (in dollars per share)									$ 0.06	$ (0.12)	$ 0.00
Earnings per common share (diluted) (in dollars per share)									$ 4.39	$ 3.55	$ 2.87