Employee Benefits - Net Pension Cost (Benefit) for All Funded and Unfunded Plans (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on PBO	$ 10	$ 12	$ 30	$ 36
Expected return on plan assets	(13)	(17)	(39)	(51)
Amortization of losses	4	4	12	12
Net pension/postretirement benefit cost	1	(1)	3	(3)
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost on PBO	1	1	1	1
Expected return on plan assets	(1)	(1)	(1)	(1)
Net pension/postretirement benefit cost	$ 0	$ 0	$ 0	$ 0