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		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivatives, Fair Value
Change in fair value of interest rate swaps hedging long-term debt	$ (6)	$ (19)	$ (13)	$ 103
Change in fair value of hedged long-term debt	$ 5	$ 17	$ 11	$ (109)