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Fair Value Measurements (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Measurements, Recurring [Member]
   
Assets:    
Commodity derivative contracts $ 176 $ 169
Physical purchase contracts (2) 17
Investments of certain benefit plans 95 114
Other investments 0 0
Liabilities:    
Commodity derivative contracts 25 39
Biofuels blending obligation   51
Obligations of certain benefit plans 34 36
Fair Value, Measurements, Nonrecurring [Member]
   
Fair Value Measurements (Textual)    
Assets, nonrecurring 0 0
Liabilities, nonrecurring 0 0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Commodity derivative contracts 2,038 3,240
Physical purchase contracts 0 0
Investments of certain benefit plans 84 104
Other investments 0 0
Liabilities:    
Commodity derivative contracts 1,864 3,097
Biofuels blending obligation   51
Obligations of certain benefit plans 34 36
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Commodity derivative contracts 78 489
Physical purchase contracts (2) 17
Investments of certain benefit plans 0 0
Other investments 0 0
Liabilities:    
Commodity derivative contracts 101 502
Biofuels blending obligation   0
Obligations of certain benefit plans 0 0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Commodity derivative contracts 0 0
Physical purchase contracts 0 0
Investments of certain benefit plans 11 10
Other investments 0 0
Liabilities:    
Commodity derivative contracts 0 0
Biofuels blending obligation   0
Obligations of certain benefit plans 0 0
Netting and Collateral [Member]
   
Fair Value Measurements (Textual)    
Cash collateral received from (payable to) brokers 136 403
Netting and Collateral [Member] | Fair Value, Measurements, Recurring [Member]
   
Assets:    
Commodity derivative contracts (1,940) (3,560)
Physical purchase contracts 0 0
Investments of certain benefit plans 0 0
Other investments 0 0
Liabilities:    
Commodity derivative contracts (1,940) (3,560)
Biofuels blending obligation   0
Obligations of certain benefit plans $ 0 $ 0