Change in the Fair Value for Interest Rate Contracts and the Related Hedged Items (Detail) - Fair Value Hedging - Interest Rate Contract - Interest Expense, Long-Term Debt - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivatives, Fair Value [Line Items]
Change in fair value of interest rate swaps hedging long-term debt	$ 64	$ (16)	$ 15	$ 48
Change in fair value of hedged long-term debt	$ (65)	$ 16	$ (18)	$ (51)