Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 25	$ 32	$ 49	$ 65
Interest cost	50	47	101	94
Expected return on plan assets	(44)	(40)	(89)	(80)
Amortization of unrecognized (gain) loss and prior service cost (credit)	2	15	5	33
Curtailment (gain) loss		2		2
Settlement (gain) loss		(1)		(1)
Total	33	55	66	113
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	4	14	9	28
Interest cost	22	28	44	56
Expected return on plan assets			(1)	(1)
Amortization of unrecognized (gain) loss and prior service cost (credit)	(20)	2	(39)	5
Total	$ 6	$ 44	$ 13	$ 88