Pension and Other Postretirement Benefit Costs Table (Detail) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	$ 20	$ 17	$ 59	$ 52
Interest cost	21	21	64	63
Expected return on plan assets	(21)	(21)	(64)	(62)
Amortization of net actuarial loss (gain)	22	14	64	49
Amortization of net prior service cost (credit)		1	1	2
Net periodic benefit cost	42	32	124	104
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	3	3	7	7
Interest cost	4	4	12	12
Amortization of net actuarial loss (gain)		(1)		(2)
Amortization of net prior service cost (credit)				(1)
Net periodic benefit cost	$ 7	$ 6	$ 19	$ 16