COMMITMENTS AND CONTINGENCIES (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Unconditional purchase obligations
Total Amounts Committed	$ 3,029.3
2013	733.7
2014	851.9
2015	333.9
2016	187.6
2017	123.1
Later Years	799.1
Natural gas utility supply and transportation | Natural Gas Utility
Unconditional purchase obligations
Total Amounts Committed	783.1
2013	83.5
2014	156.7
2015	138.5
2016	126.0
2017	86.9
Later Years	191.5
Purchased power | Electric Utility
Unconditional purchase obligations
Total Amounts Committed	810.0
2013	79.4
2014	40.0
2015	31.9
2016	28.7
2017	27.7
Later Years	602.3
Coal supply and transportation | Electric Utility
Unconditional purchase obligations
Total Amounts Committed	116.5
2013	29.4
2014	44.2
2015	31.5
2016	7.2
2017	4.2
Later Years	0
Nonregulated electricity and natural gas supply | Nonutility and Nonregulated Operations
Unconditional purchase obligations
Total Amounts Committed	1,319.7
2013	541.4
2014	611.0
2015	132.0
2016	25.7
2017	4.3
Later Years	5.3
Purchase Order
Purchase and sales commitments
Supply contract obligation amount	$ 722.3