Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 32	$ 25	$ 65	$ 50
Interest cost	47	46	94	92
Expected return on plan assets	(40)	(35)	(80)	(70)
Amortization of unrecognized (gain) loss and prior service cost	15	6	33	11
Curtailment loss	2		2
Settlement gain	(1)		(1)
Total	55	42	113	83
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	14	13	28	26
Interest cost	28	32	56	63
Expected return on plan assets		(1)	(1)	(2)
Amortization of unrecognized (gain) loss and prior service cost	2	(1)	5	(2)
Total	$ 44	$ 43	$ 88	$ 85