COMMITMENTS AND CONTINGENCIES (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Minimum future commitments for purchase obligations
Total Amounts Committed	$ 1,136.5
2014	168.6
2015	106.6
2016	80.3
2017	72.1
2018	67.8
Later Years	641.1
Purchase Orders	484.4
Purchased power | Electric Utility
Minimum future commitments for purchase obligations
Total Amounts Committed	762.4
2014	75.4
2015	32.2
2016	28.2
2017	26.9
2018	26.3
Later Years	573.4
Coal supply and transportation | 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
Natural gas utility supply and transportation | Natural Gas Utility
Minimum future commitments for purchase obligations
Total Amounts Committed	274.6
2014	46.9
2015	43.4
2016	40.1
2017	38.5
2018	38.0
Later Years	$ 67.7