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, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Fair Value Hedging | Interest Rate Contract | Interest Expense, Long-Term Debt
Derivatives, Fair Value [Line Items]
Change in fair value of interest rate swaps hedging long-term debt	$ 41	$ 35
Change in fair value of hedged long-term debt	$ (43)	$ (37)