Retirement Plans - Components of Net Periodic Pension Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Compensation And Retirement Disclosure [Abstract]
Service cost	$ 12	$ 10	$ 33	$ 34
Interest cost	23	24	71	71
Expected return on plan assets	(45)	(49)	(135)	(147)
Amortization of unrecognized net actuarial losses	13	8	36	29
Settlement loss	88	0	88	0
Curtailment gains	0	0	0	(2)
Pension (income) expense	$ 91	$ (7)	$ 93	$ (15)