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Operating Revenue (Operating Revenue) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Electric sales:    
Regulated $ 1,724 $ 1,730
Nonregulated 738 941
Gas sales:    
Regulated 99 139
Nonregulated 398 602
Gas transportation and storage 405 538
Other 128 107
Total operating revenue $ 3,492 $ 4,057