Net Periodic Benefit Cost (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
Service cost	$ 18	$ 17	$ 53	$ 52
Interest cost	32	33	97	97
Expected return on plan assets	(47)	(46)	(142)	(137)
Amortization of prior service cost	(5)	(3)	(14)	(9)
Recognized net actuarial loss	11	16	32	46
Net periodic benefit cost	9	17	26	49
Other Postretirement Benefit Plans, Defined Benefit
Service cost	0	0	0	0
Interest cost	3	3	7	7
Expected return on plan assets	(2)	(2)	(6)	(6)
Amortization of prior service cost	0	0	0	0
Recognized net actuarial loss	0	0	1	1
Net periodic benefit cost	$ 1	$ 1	$ 2	$ 2