Annual report pursuant to Section 13 and 15(d)

Income Taxes - Net Operating Loss and Tax Credit Carryforwards (Details)

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Income Taxes - Net Operating Loss and Tax Credit Carryforwards (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Tax Credit Carryforward [Line Items]    
Deferred Tax Asset $ 2,707 $ 5,614
Operating Loss Carryforwards [Line Items]    
Deferred Tax Asset 9,494 $ 10,955
Net operating losses before benefit of federal deductions 1,400  
Valuation allowance before considering benefit of federal deductions 623  
Net operating losses – U.S.    
Operating Loss Carryforwards [Line Items]    
Deferred Tax Asset 2,507  
Valuation Allowance 0  
Net Deferred Tax Asset 2,507  
Net operating losses – U.K. and other    
Operating Loss Carryforwards [Line Items]    
Deferred Tax Asset 432  
Valuation Allowance (323)  
Net Deferred Tax Asset 109  
Net operating losses – U.S. states    
Operating Loss Carryforwards [Line Items]    
Deferred Tax Asset 898  
Valuation Allowance (405)  
Net Deferred Tax Asset 493  
General business credits    
Tax Credit Carryforward [Line Items]    
Deferred Tax Asset 2,635  
Valuation Allowance 0  
Net Deferred Tax Asset 2,635  
Foreign tax credits    
Tax Credit Carryforward [Line Items]    
Deferred Tax Asset 72  
Valuation Allowance (72)  
Net Deferred Tax Asset 0  
UNITED KINGDOM | Net operating losses – U.K. and other    
Operating Loss Carryforwards [Line Items]    
Deferred Tax Asset 5,657  
Valuation Allowance 0  
Net Deferred Tax Asset $ 5,657