DERIVATIVE FINANCIAL INSTRUMENTS (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2011 Dekatherm	Dec. 31, 2010 Dekatherm
Natural Gas Derivative Contracts and Interest Rate Swaps Outstanding
Commodity and other energy management contracts designated as cash flow hedges (in DT)	24,195,098	22,905,351
Commodity and other energy management contracts not designated as hedges (in DT)	33,396,436	31,265,581
Commodity and other energy management contracts (in DT)	57,591,534	54,170,932
Aggregate notional amount of interest rate swaps designated as fair value hedge (in dollars)	$ 253.2	$ 556.4
Aggregate notional amount of interest rate swaps designated as cash flow hedge (in dollars)	$ 572.6	$ 1,100.0
Gas Distribution
Natural Gas Derivative Contracts and Interest Rate Swaps Outstanding
Commodity and other energy management contracts not designated as hedges (in DT)	10,014,000	10,677,000
Commodity and other energy management contracts (in DT)	10,014,000	10,677,000
Retail Gas Marketing
Natural Gas Derivative Contracts and Interest Rate Swaps Outstanding
Commodity and other energy management contracts designated as cash flow hedges (in DT)	5,524,000	5,715,000
Commodity and other energy management contracts (in DT)	5,524,000	5,715,000
Energy Marketing
Natural Gas Derivative Contracts and Interest Rate Swaps Outstanding
Commodity and other energy management contracts designated as cash flow hedges (in DT)	18,671,098	17,190,351
Commodity and other energy management contracts not designated as hedges (in DT)	23,382,436	20,588,581
Commodity and other energy management contracts (in DT)	42,053,534	37,778,932
Basis swap contracts in Energy Marketing (in DT)	8,019,000	6,485,536