Rate and Regulatory Matters (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Details of Other regulatory assets
Other regulatory assets	$ 4,636,871	$ 3,838,237
Asset Retirement Obligation [Member]
Details of Other regulatory assets
Other regulatory assets	395,900	406,400
Deferred Capacity [Member]
Details of Other regulatory assets
Other regulatory assets	0	15,800
Fuel Non-current [Member]
Details of Other regulatory assets
Other regulatory assets	12,400	17,400
Gas Hedging [Member]
Details of Other regulatory assets
Other regulatory assets	30,300	1,900
New Nuclear Generation Development Costs [Member]
Details of Other regulatory assets
Other regulatory assets	56,800
Pension & Postretirement Costs [Member]
Details of Other regulatory assets
Other regulatory assets	2,542,000	1,734,700
Postretirement Benefit Costs [Member]
Details of Other regulatory assets
Other regulatory assets	2,400	4,800
Storm Costs [Member]
Details of Other regulatory assets
Other regulatory assets	996,400	1,026,000
Removal Costs [Member]
Details of Other regulatory assets
Other regulatory assets	81,200	81,500
River Bend AFUDC [Member]
Details of Other regulatory assets
Other regulatory assets	24,300	26,200
Sale-leaseback Deferral [Member]
Details of Other regulatory assets
Other regulatory assets	0	22,300
Spindletop Gas Storage Facility [Member]
Details of Other regulatory assets
Other regulatory assets	31,000	32,600
Competitive Transition Charge [Member]
Details of Other regulatory assets
Other regulatory assets	89,200	95,800
Little Gypsy Repowering Project Costs [Member]
Details of Other regulatory assets
Other regulatory assets	198,400	200,900
Loss on Reacquired Debt [Member]
Details of Other regulatory assets
Other regulatory assets	108,800	122,500
Other Regulatory Asset [Member]
Details of Other regulatory assets
Other regulatory assets	44,400	38,300
Incremental ice storm costs [Member]
Details of Other regulatory assets
Other regulatory assets	10,500	11,100
Michoud plant maintenance [Member]
Details of Other regulatory assets
Other regulatory assets	$ 12,900	$ 0