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Statements of Consolidated Comprehensive Income (Parenthetical) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Statements of Consolidated Comprehensive Income    
Natural gas, tax (benefit) expense $ (14,896) $ (51,583)
Interest rate, tax expense 25 25
Pension and other post-retirement benefits liability adjustment, tax expense $ 114 $ 307