Risk Management and Fair Values (Derivative Instruments Designated As Cash Flow Hedges On Consolidated Statements Of Income) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Effect of Derivative instruments designated as cash flow hedges on consolidated statements of income
Amount of gain reclassified from accumulated OCI into income (effective portion)	$ 71,000	$ 29,000
Competitive Businesses Operating Revenues [Member] | Electricity Forwards, Swaps And Options [Member] | Cash Flow Hedging [Member]
Effect of Derivative instruments designated as cash flow hedges on consolidated statements of income
Amount of gain (loss) recognized in AOCI (effective portion)	291,000	(74,000)
Amount of gain reclassified from accumulated OCI into income (effective portion)	$ 71,000	$ 29,000