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	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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	$ 120	$ (279)	$ (104)
Change in fair value of hedged long-term debt	$ (126)	$ 276	$ 107