Derivative instruments (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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	$ 34	$ (48)	$ (181)
Offsetting unrealized gain (loss) on related interest rate swaps	(34)	48	181
Foreign currency option contracts [Member] | Derivatives designated as hedging instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount	608	225	271
Foreign currency forward and option contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount of terminated derivatives		2,300
Foreign currency forward and option contracts [Member] | Net cash provided by operating activities [Member]
Derivative Instruments Gain Loss [Line Items]
Proceeds from counterparties on termination of derivatives		340
Foreign currency and cross currency swap contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Amounts expected to be reclassified from accumulated other comprehensive income into earnings over the next 12 months - gains on foreign currency and cross currency swap	80
Forward interest rate contracts [Member]
Derivative Instruments Gain Loss [Line Items]
Amounts expected to be reclassified from accumulated other comprehensive income into earnings over the next 12 months - gain (loss)	2
Interest rate swap [Member] | Derivatives designated as hedging instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount	6,650	6,650	6,650
Foreign currency forward contracts [Member] | Derivatives designated as hedging instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount	3,400	3,300	3,800
Foreign currency forward contracts [Member] | Derivatives not designated as hedging instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount	$ 666	$ 911	$ 875
Minimum [Member] | Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member] | Three-Month LIBOR [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, effective interest rate	0.40%
Maximum [Member] | Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member] | Three-Month LIBOR [Member]
Derivative Instruments Gain Loss [Line Items]
Derivative, effective interest rate	2.00%