Benefit or Income Cost Related to Pension and Postretirement Health Care and Life Insurance Plans (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 93	$ 82	$ 280	$ 245
Amortization of prior service credit	(1)	(2)	(3)	(6)
Expected return on plan assets	(317)	(296)	(952)	(886)
Interest cost	242	259	727	777
Remeasurement loss, net	342		342
Total	359	43	394	130
Health Care And Life
Defined Benefit Plan Disclosure [Line Items]
Service cost	81	65	243	194
Amortization of prior service credit	(72)	(63)	(215)	(190)
Expected return on plan assets	(25)	(41)	(76)	(122)
Interest cost	280	277	838	831
Total	$ 264	$ 238	$ 790	$ 713