Pension and Other Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Frequency of asset performance monitored, years	5 years
Anticipated contributions to postretirement benefit plans	$ 650
Expenses for deferred benefit programs	620	582	403
Postretirement medical plan [Member] | US [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Investment of assets in government and government-related debt securities under US postretirement medical plan	63.00%
Postretirement medical plan [Member] | Government and government-related debt securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Investment of assets in government and government-related debt securities under US postretirement medical plan	37.00%
Minimum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Range of expected benefits to be paid for the annual pension and postretirement medical plans (net of the annual Medicare Part D subsidy)	4
Maximum [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Range of expected benefits to be paid for the annual pension and postretirement medical plans (net of the annual Medicare Part D subsidy)	$ 11