COMMITMENTS AND CONTINGENCIES (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Unconditional purchase obligations
Total Amounts Committed	$ 2,380.5
2013	253.4
2014	611.6
2015	338.3
2016	222.8
2017	143.2
Later Years	811.2
Natural gas utility supply and transportation | Natural Gas Utility
Unconditional purchase obligations
Total Amounts Committed	839.8
2013	48.5
2014	171.0
2015	162.4
2016	148.5
2017	103.4
Later Years	206.0
Purchased power | Electric Utility
Unconditional purchase obligations
Total Amounts Committed	795.5
2013	37.6
2014	66.5
2015	32.6
2016	28.8
2017	27.7
Later Years	602.3
Coal supply and transportation | Electric Utility
Unconditional purchase obligations
Total Amounts Committed	110.6
2013	17.3
2014	44.4
2015	31.9
2016	9.5
2017	6.0
Later Years	1.5
Nonregulated electricity and natural gas supply | Nonutility and Nonregulated Operations
Unconditional purchase obligations
Total Amounts Committed	634.6
2013	150.0
2014	329.7
2015	111.4
2016	36.0
2017	6.1
Later Years	1.4
Purchase Order
Purchase and sales commitments
Commitments in the form of purchase orders issued to vendors	$ 770.9