Employee Benefit Plans (Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost		$ 3	$ 4	$ 7	$ 8
Interest cost		7	7	15	15
Expected return on assets		(10)	(12)	(20)	(24)
Amortization of actuarial losses		3	3	7	5
Curtailment	[1]	6	0	6	0
Net periodic benefit cost		9	2	15	4
Other Postretirement Benefits
Components of Net Periodic Benefit Cost
Service cost		0	1	1	2
Interest cost		2	2	4	4
Expected return on assets		0	0	0	0
Amortization of actuarial losses		0	1	0	1
Curtailment	[1]	3	0	3	0
Net periodic benefit cost		$ 5	$ 4	$ 8	$ 7

[1] Related to a voluntary retirement program.