Retirement Plans and Other Post-Retirement Benefits - Schedule of Net Periodic Costs of Pension and Post Retirement Medical Benefit Plans Included in Continuing Operations (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 484	$ 594
Interest cost	3,450	3,241
Expected return on plan assets	(3,696)	(5,531)
Amortization of prior service cost/(credit)	34	5
Amortization of unrecognized/actuarial loss (gain)	775	2,060
Total net periodic benefit cost	1,047	369
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	15
Interest cost	84	80
Amortization of prior service cost/(credit)	(2)
Amortization of unrecognized/actuarial loss (gain)	(173)	(16)
Total net periodic benefit cost	$ (82)	$ 79