Stockholders' equity Stockholders' equity (Details 1) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Increase (Decrease) in Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance, Foreign currency translation	$ 21	$ 22	$ 40
Beginning balance, Cash flow hedges	43	3	(82)
Beginning balance, Available-for-sale securities	120	135	95
Beginning balance, Other	(13)	(7)	(8)
Beginning balance, AOCI	171	153	45
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign currency translation adjustments	(13)	(6)	(29)
Unrealized gains (losses), Cash flow hedges	15	(51)	186
Unrealized gains (losses), Available-for-sale securities	233	125	155
Unrealized gains (losses), Other	(1)	2	1
Unrealized gains (losses), Accumulated other comprehensive income	247	76	342
Reclassification adjustments to income, Cash flow hedges	(134)	112	(46)
Reclassification adjustments to income, Available-for-sale securities	(132)	(154)	(90)
Reclassification adjustments to income, Accumulated other comprehensive income	(266)	(42)	(136)
Other		(8)
Other, Accumulated other comprehensive income		(8)
Income taxes, Foreign currency translation	4	5	11
Income taxes, Cash flow hedges	41	(21)	(55)
Income taxes, Available-for-sale securities	(38)	14	(25)
Income taxes, Other	0	0	0
Income taxes, Accumulated other comprehensive income (loss)	7	(2)	(69)
Ending balance, Foreign currency translation	12	21	22
Ending balance, Cash flow hedges	(35)	43	3
Ending balance, Available-for-sale securities	183	120	135
Ending balance, Other	(14)	(13)	(7)
Ending balance, AOCI	$ 146	$ 171	$ 153