Stockholders' equity (Components of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended
Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period			$ 29,875
Balance as of end of period	$ 32,229
Foreign currency translation [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	(551)	$ (586)	(610)
OCI, before reclassifications, before tax	38	37	21
Income taxes	3	(2)	3
Balance as of end of period	(510)	(551)	(586)
Accumulated net gain (loss) from cash flow hedges [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	8	209	282
OCI, before reclassifications, before tax	65	17	17
Reclassification adjustments to income	(140)	(330)	(131)
Income taxes	25	112	41
Balance as of end of period	(42)	8	209
Available-for-sale securities [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	100	20	(138)
OCI, before reclassifications, before tax	41	73	116
Reclassification adjustments to income	(26)	47	49
Income taxes	(6)	(40)	(7)
Balance as of end of period	109	100	20
Accumulated Other Adjustment Attributable to Parent [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	(6)	(5)	(5)
OCI, before reclassifications, before tax	0	0	0
Other	6	(1)
Balance as of end of period	0	(6)	(5)
AOCI [Member]
Increase (Decrease) in AOCI [Roll Forward]
Balance as of beginning of period	(449)	(362)	(471)
OCI, before reclassifications, before tax	106	90	133
Reclassification adjustments to income	(166)	(283)	(82)
Other	6	(1)
Income taxes	22	70	37
Balance as of end of period	$ (443)	$ (449)	$ (362)

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 14A
-URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580

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Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Amount before tax of reclassification adjustments of other comprehensive income (loss) attributable to parent.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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