Derivatives (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
	Mar. 31, 2017	Mar. 31, 2016
Derivatives, Fair Value
Change in fair value of interest rate swaps hedging long-term debt	$ (21)	$ 83
Change in fair value of hedged long-term debt	$ 21	$ (85)