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Schedule of Cash Flow Hedges Effect on Accumulated Other Comprehensive Income, Net of Taxes (Detail) - Cash Flow Hedges - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]        
Accumulated gain / (loss) at beginning of period $ (46) $ 82 $ (2) $ 117
Transfer of realized losses / (gains) in fair value to earnings (36) (2) (54) (3)
Unrealized gain / (loss) in fair value 29 (36) 3 (70)
Accumulated gain / (loss) at end of period $ (53) $ 44 $ (53) $ 44