Pension Plans, Other Postretirement Benefits, and Defined-Contribution Plans - Components of Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Income (Expense) Table (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	$ 76	$ 78	$ 69
Interest cost	85	85	84
Expected return on plan assets	(91)	(85)	(80)
Amortization of net actuarial loss (gain)	93	85	65
Amortization of net prior service cost (credit)		2	3
Net periodic benefit cost	163	165	141
Amounts recognized in other comprehensive income (expense)
Net actuarial gain (loss)	(156)	(183)	(151)
Amortization of net actuarial (gain) loss	93	85	65
Net prior service (cost) credit		12	(6)
Amortization of net prior service cost (credit)		2	3
Total amounts recognized in other comprehensive income (expense)	(63)	(84)	(89)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost	9	9	9
Interest cost	16	16	16
Amortization of net actuarial loss (gain)			(3)
Amortization of net prior service cost (credit)	2		(1)
Net periodic benefit cost	27	25	21
Amounts recognized in other comprehensive income (expense)
Net actuarial gain (loss)	1	(30)	8
Amortization of net actuarial (gain) loss			(3)
Amortization of net prior service cost (credit)	2		(1)
Total amounts recognized in other comprehensive income (expense)	$ 3	$ (30)	$ 4