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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 373	$ 595	$ 857	$ 1,189
Interest cost	3,337	3,241	6,787	6,482
Expected return on plan assets	(3,699)	(5,530)	(7,395)	(11,061)
Amortization of prior service cost/(credit)	54	4	88	11
Amortization of unrecognized/actuarial loss (gain)	789	2,060	1,564	4,119
Total net periodic benefit cost	854	370	1,901	740
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	15	18	30
Interest cost	84	79	168	159
Amortization of prior service cost/(credit)	(3)		(5)
Amortization of unrecognized/actuarial loss (gain)	(173)	(17)	(346)	(33)
Total net periodic benefit cost	$ (83)	$ 77	$ (165)	$ 156