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Net of Tax Activity in Accumulated Other Comprehensive Income Related to Cash Flow Hedges (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]      
Hedging activities, Beginning Balance $ 3 $ 7 $ 34
Amount reclassified to earnings during the year 5 (5) (31)
Hedging activities, Ending Balance (10) 3 7
Continuing Operations      
Accumulated Other Comprehensive Income (Loss) [Line Items]      
(Loss) gain in fair value of derivatives during the year $ (18) $ 1 $ 4