Fair Value Hedges (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Interest Rate Swap
Derivative Instruments, Gain (Loss) [Line Items]
Gain / (loss) recognized in income on fair value of hedges	$ (2)	$ (11)	$ (4)	$ (2)
Long-term Debt
Derivative Instruments, Gain (Loss) [Line Items]
Gain / (loss) recognized in income on fair value of hedges	$ 2	$ 11	$ 4	$ 2