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Income Taxes - Additional Information (Detail) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2015
Mar. 31, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Dec. 31, 2015
Dec. 31, 2014
Income Tax Contingency [Line Items]              
Impact on provision for income tax, out-of-period adjustments $ 4   $ 5 $ 11 $ 5    
Effective tax rate 19.00%   12.40% 22.40% 7.50%   19.60%
Total favorable discrete items $ 8   $ 52 $ 33 $ 104    
Net unfavorable tax charge related to the sale of joint venture 22 $ 32   54      
Net favorable tax audit settlements and expirations of statutes of limitations $ 11   9 $ 33 60    
Tax return to provision adjustments     $ 37   $ 37    
Scenario, Forecast              
Income Tax Contingency [Line Items]              
Estimated effective tax rate           19.00%