DERIVATIVE FINANCIAL INSTRUMENTS (Details) (USD $) In Millions, unless otherwise specified	Sep. 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)	31,910,325	22,905,351
Commodity and other energy management contracts not designated as hedges (in DT)	34,333,870	31,265,581
Commodity and other energy management contracts (in DT)	66,244,195	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)	10,118,000	10,677,000
Commodity and other energy management contracts (in DT)	10,118,000	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)	9,060,000	5,715,000
Commodity and other energy management contracts (in DT)	9,060,000	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)	22,850,325	17,190,351
Commodity and other energy management contracts not designated as hedges (in DT)	24,215,870	20,588,581
Commodity and other energy management contracts (in DT)	47,066,195	37,778,932
Basis swap contracts in Energy Marketing (in DT)	9,098,000	6,485,536