Commitments: (Details 2) (USD $) In Millions, unless otherwise specified			6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Extended warranty	Jun. 30, 2011 Extended warranty
Movement in extended warranty liability
Beginning balance, aggregate deferred revenue			$ 636	$ 670
Revenue deferred for new extended warranty contracts			127	141
Amortization of deferred revenue			(154)	(164)
Other			(6)	2
Ending balance, aggregate deferred revenue			602	649
Deferred revenue:
Deferred income, current portion	12,311	12,197	288	309
Deferred income, noncurrent portion	3,889	3,847	314	340
Aggregate deferred revenue			$ 602	$ 649