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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 216	$ 595	$ 1,073	$ 1,784
Interest cost	3,287	3,241	10,074	9,723
Expected return on plan assets	(3,895)	(5,531)	(11,290)	(16,592)
Amortization of prior service cost/(credit)	64	5	152	16
Amortization of unrecognized/actuarial loss (gain)	819	2,060	2,383	6,179
Total net periodic benefit cost	491	370	2,392	1,110
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	16	25	46
Interest cost	67	80	235	239
Amortization of prior service cost/(credit)	(2)		(7)
Amortization of unrecognized/actuarial loss (gain)	(293)	(16)	(639)	(49)
Total net periodic benefit cost	$ (221)	$ 80	$ (386)	$ 236