Pension Plans and Other Postretirement Benefits (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	$ 21	$ 19	$ 64	$ 57
Interest cost	19	21	58	64
Expected return on plan assets	(22)	(23)	(68)	(68)
Amortization of net actuarial loss (gain)	29	23	88	69
Amortization of net prior service cost (credit)	0	0	0	0
Net periodic benefit cost	47	40	142	122
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	2	2	7	7
Interest cost	3	4	10	12
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss (gain)	0	0	0	0
Amortization of net prior service cost (credit)	1	0	1	1
Net periodic benefit cost	$ 6	$ 6	$ 18	$ 20