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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 595	$ 487	$ 1,784	$ 1,462
Interest cost	3,241	3,413	9,723	10,240
Expected return on plan assets	(5,531)	(5,514)	(16,592)	(16,542)
Amortization of prior service cost/(credit)	5	7	16	17
Amortization of unrecognized/actuarial loss (gain)	2,060	1,777	6,179	5,332
Total net periodic benefit cost	370	170	1,110	509
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	16	16	46	49
Interest cost	80	91	239	275
Amortization of unrecognized/actuarial loss (gain)	(16)	(4)	(49)	(10)
Total net periodic benefit cost	$ 80	$ 103	$ 236	$ 314