Pension and Other Benefit Plans - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Frequency of asset performance monitored, years	5 years
Anticipated contributions to postretirement benefit plans	$ 500
Expenses for deferred benefit programs	671	620	582
Minimum
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
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)	$ 9
Postretirement medical plan | US
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Investment of assets in government and government-related debt securities under US postretirement medical plan	61.00%
Postretirement medical plan | Government and government-related debt securities
Pension Plans Postretirement And Other Employee Benefits [Line Items]
Investment of assets in government and government-related debt securities under US postretirement medical plan	39.00%