Derivative instruments (Details Textual) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Derivative Instruments Gain Loss [Line Items]
Length of time hedged in foreign currency contracts			3 years
Interest expense, net [Member]
Derivative Instruments Gain Loss [Line Items]
Unrealized gain (loss) on the hedged debt	$ 61	$ (134)	$ (137)	$ (140)
Unrealized gain (loss) on interest rate swaps	(61)	$ 134	137	$ 140
Foreign currency forward contracts [Member] | Derivatives designated as hedging instrument [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount	3,500		3,500		$ 3,300
Foreign currency forward contracts [Member] | Derivatives not designated as hedging instrument [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount	874		874		911
Foreign currency option contracts [Member] | Derivatives designated as hedging instrument [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount	178		178		225
Forward interest rate contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Amounts expected to be reclassified from AOCI into earnings over the next 12 months	(2)		(2)
Foreign currency and cross currency swap contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Amounts expected to be reclassified from AOCI into earnings over the next 12 months	39		39
Interest rate swap [Member] | Derivatives designated as hedging instrument [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, notional amount	$ 6,650		$ 6,650		$ 6,650
Rate adjustment to LIBOR on interest rate swap agreements [Member] | LIBOR [Member] | Minimum [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, variable interest rate	0.40%		0.40%		0.40%
Rate adjustment to LIBOR on interest rate swap agreements [Member] | LIBOR [Member] | Maximum [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, variable interest rate	2.00%		2.00%		2.00%