COMMITMENTS AND CONTINGENCIES (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Minimum future commitments for purchase obligations
Total Amounts Committed	$ 2,415.6
2014	800.9
2015	378.6
2016	249.1
2017	164.4
2018	103.7
Later Years	718.9
Purchase Orders	909.0
Natural gas utility supply and transportation | Regulated operations | Natural Gas Utility
Minimum future commitments for purchase obligations
Total Amounts Committed	845.9
2014	181.2
2015	169.6
2016	158.4
2017	122.0
2018	71.7
Later Years	143.0
Purchased power | Regulated operations | Electric Utility
Minimum future commitments for purchase obligations
Total Amounts Committed	772.3
2014	80.6
2015	32.8
2016	28.8
2017	27.6
2018	27.0
Later Years	575.5
Coal supply and transportation | Regulated operations | Electric Utility
Minimum future commitments for purchase obligations
Total Amounts Committed	99.5
2014	46.3
2015	31.0
2016	12.0
2017	6.7
2018	3.5
Later Years	0
Nonregulated electricity and natural gas supply | Nonutility and nonregulated operations | Integrys Energy Services
Minimum future commitments for purchase obligations
Total Amounts Committed	697.9
2014	492.8
2015	145.2
2016	49.9
2017	8.1
2018	1.5
Later Years	0.4
UPPCO | Regulated operations | Electric Utility
Minimum future commitments for purchase obligations
Purchase Orders	12.2
UPPCO | Purchased power | Regulated operations | Electric Utility
Minimum future commitments for purchase obligations
Total Amounts Committed	$ 9.9