Components of Net Periodic Benefit Cost (credit) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3	$ 3	$ 9	$ 9
Interest cost	2	1	5	4
Expected return on assets	(2)	(1)	(6)	(5)
Prior service cost	0	0	0	0
Net periodic benefit cost (credit)	3	3	8	8
Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1	1
Interest cost	1	2	3	5
Expected return on assets	0	0	0	0
Prior service cost	(3)	(1)	(10)	(3)
Net periodic benefit cost (credit)	$ (2)	$ 1	$ (6)	$ 3