Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 24	$ 29	$ 73	$ 94
Interest cost	50	48	151	142
Expected return on plan assets	(45)	(41)	(134)	(121)
Amortization of unrecognized (gain) loss and prior service cost (credit)	3	8	8	41
Curtailment loss				2
Settlement gain	(1)	(1)	(1)	(2)
Total	31	43	97	156
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	14	14	42
Interest cost	22	29	66	85
Expected return on plan assets	(1)	(1)	(2)	(2)
Amortization of unrecognized (gain) loss and prior service cost (credit)	(19)	2	(58)	7
Total	$ 7	$ 44	$ 20	$ 132