Employee Benefit Plans (Net Periodic Benefit Cost (Credit) (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Components of Net Periodic Benefit Cost
Service cost		$ 4	$ 5	$ 11	$ 13
Interest cost		6	7	21	22
Expected return on assets		(11)	(12)	(31)	(36)
Amortization of actuarial losses (gains)		2	3	9	8
Curtailment	[1]			6	0
Settlement loss	[1]	11	0	11	0
Net periodic benefit cost		12	3	27	7
Other Postretirement Benefits
Components of Net Periodic Benefit Cost
Service cost		1	1	2	3
Interest cost		2	2	6	6
Expected return on assets		0	0	0	0
Amortization of actuarial losses (gains)		0	(1)	0	0
Curtailment	[1]			3	0
Settlement loss	[1]	0	0	0	0
Net periodic benefit cost		$ 3	$ 2	$ 11	$ 9

[1] Related to a voluntary retirement program.