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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivatives, Fair Value
Change in fair value of interest rate swaps hedging long-term debt	$ 14	$ 39	$ (6)	$ 122
Change in fair value of hedged long-term debt	$ (15)	$ (41)	$ 5	$ (126)