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Income Taxes (Tables)
 6 Months Ended
Jun. 30, 2011
Income Tax Disclosure [Abstract]  
Factors Causing Variation in Effective Tax Rate From US Federal Statutory Rate
The differences that caused our effective income tax rates to vary from the 35% U.S. federal statutory rate for income taxes were as follows:
 
Six Months Ended
 
June 30,
 
2011
 
2010
 
(in millions)
Income tax benefit at the federal statutory rate
$
403


 
$
527


Effect of:
 
 
 
State income taxes, net of federal income tax effect
(10
)
 
46


Change in valuation allowance
(533
)
 
(667
)
Other, net
4


 
(24
)
Income tax expense
$
(136
)
 
$
(118
)
Effective income tax rate
(11.8
)%
 
(7.8
)%