Net of Tax Activity in Accumulated Other Comprehensive Income Related to Cash Flow Hedges (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Hedging activities, Beginning Balance	$ 34		$ 10		$ (5)
Gain in fair value of derivatives during the year	46		32
Amount reclassified to earnings during the year	(31)	[1]	(8)	[1]	(26)
Hedging activities, Ending Balance	7		34		10
Continuing Operations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gain in fair value of derivatives during the year	$ 4		$ 32		$ 41

[1] Amounts in parentheses indicate reductions to net income.