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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivatives, Fair Value [Line Items]
Change in fair value of interest rate swaps hedging long-term debt	$ (90)	$ 29	$ (49)	$ 64
Change in fair value of hedged long-term debt	$ 90	$ (30)	$ 48	$ (67)