Pension Plans and Other Postretirement Benefits (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 Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	$ 22	$ 19	$ 43	$ 38
Interest cost	19	22	39	43
Expected return on plan assets	(23)	(22)	(46)	(45)
Amortization of net actuarial loss (gain)	30	23	59	46
Net periodic benefit cost	48	42	95	82
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	3	3	5	5
Interest cost	3	4	7	8
Amortization of net prior service cost (credit)		1		1
Net periodic benefit cost	$ 6	$ 8	$ 12	$ 14