Pension Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost Table (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	$ 19	$ 20	$ 57	$ 59
Interest cost	21	21	64	64
Expected return on plan assets	(23)	(21)	(68)	(64)
Amortization of net actuarial loss (gain)	23	22	69	64
Amortization of net prior service cost (credit)				1
Net periodic benefit cost	40	42	122	124
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	2	3	7	7
Interest cost	4	4	12	12
Amortization of net prior service cost (credit)			1
Net periodic benefit cost	$ 6	$ 7	$ 20	$ 19