v2.4.0.8
Shareholders' Equity (Details 3) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Significant reclassifications from accumulated other comprehensive income to net income        
Net periodic benefit costs $ (35) $ (30) $ (69) $ (62)
Operating and maintenance costs
        
Significant reclassifications from accumulated other comprehensive income to net income        
Net periodic benefit costs (10) (8) (21) (17)
General and administrative costs
        
Significant reclassifications from accumulated other comprehensive income to net income        
Net periodic benefit costs (3) (2) (6) (6)
Defined benefit pension plans | Amount Reclassified from Accumulated Other Comprehensive Income
        
Significant reclassifications from accumulated other comprehensive income to net income        
Actuarial losses 14 11 28 22
Prior service costs (1) (1) (1) (1)
Settlements and curtailments       2
Net periodic benefit costs 13 10 27 23
Income tax benefit (1)   (2) (1)
Total amortization, net of income taxes $ 12 $ 10 $ 25 $ 22