Segments: (Revenue by segments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 23,720	$ 24,747	$ 72,052	$ 75,203
Total reportable segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	25,461	26,570	77,383	80,561
Internal transactions
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	(1,863)	(1,976)	(5,710)	(5,848)
Other revenue adjustments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 122	$ 154	$ 378	$ 490