Derivative instruments (Details Textual) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	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]
Offsetting unrealized gain (loss) on related interest rate swaps	$ (85)	$ (34)	$ 48
Unrealized gain (loss) on the hedged debt	85	34	(48)
Foreign currency option contracts [Member] | Derivatives designated as hedging instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount	74	608	225
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	175
Interest rate swap [Member] | Derivatives designated as hedging instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount	9,450	6,650
Foreign currency forward contracts [Member] | Derivatives designated as hedging instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount	4,600	3,400	3,300
Foreign currency forward contracts [Member] | Derivatives not designated as hedging instruments [Member]
Derivative Instruments Gain Loss [Line Items]
Notional amount	$ 757	$ 666	$ 911