DERIVATIVE FINANCIAL INSTRUMENTS (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011 Dth	Dec. 31, 2010 Dth
Natural Gas Derivative Contracts and Interest Rate Swaps Outstanding
Commodity and other energy management contracts designated as cash flow hedges (in DT)	36,427,763	22,905,351
Commodity and other energy management contracts not designated as hedges (in DT)	41,023,563	31,265,581
Commodity and other energy management contracts (in DT)	77,451,326	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)	$ 822.6	$ 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)	9,080,000	10,677,000
Commodity and other energy management contracts (in DT)	9,080,000	10,677,000
Retail Gas Marketing and Energy Marketing
Natural Gas Derivative Contracts and Interest Rate Swaps Outstanding
Basis swap contracts in Energy Marketing (in DT)		6,485,536
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)	6,566,000	5,715,000
Commodity and other energy management contracts (in DT)	6,566,000	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)	29,861,763	17,190,351
Commodity and other energy management contracts not designated as hedges (in DT)	31,943,563	20,588,581
Commodity and other energy management contracts (in DT)	61,805,326	37,778,932
Basis swap contracts in Energy Marketing (in DT)	9,626,000