Derivative instruments (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended						12 Months Ended					3 Months Ended
	Dec. 31, 2013	Dec. 31, 2013 Interest expense, net [Member]	Dec. 31, 2012 Interest expense, net [Member]	Dec. 31, 2011 Interest expense, net [Member]	Dec. 31, 2013 Foreign currency and cross currency swap contracts [Member]	Dec. 31, 2013 Forward interest rate contracts [Member]	Dec. 31, 2012 Interest rate swap [Member]	Dec. 31, 2013 Interest rate swap [Member]	Dec. 31, 2011 Interest rate swap [Member]	Dec. 31, 2013 Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member]	Dec. 31, 2011 Rate adjustment to LIBOR on Interest Rate Swap Agreements [Member]	Jun. 30, 2012 Net cash provided by operating activities [Member]	Dec. 31, 2013 Derivatives designated as hedging instrument [Member] Foreign currency option contracts [Member]	Dec. 31, 2012 Derivatives designated as hedging instrument [Member] Foreign currency option contracts [Member]	Dec. 31, 2011 Derivatives designated as hedging instrument [Member] Foreign currency option contracts [Member]	Dec. 31, 2013 Derivatives designated as hedging instrument [Member] Interest rate swap [Member]	Dec. 31, 2011 Derivatives designated as hedging instrument [Member] Interest rate swap [Member]	Dec. 31, 2013 Derivatives designated as hedging instrument [Member] Foreign currency forward contracts [Member]	Dec. 31, 2012 Derivatives designated as hedging instrument [Member] Foreign currency forward contracts [Member]	Dec. 31, 2011 Derivatives designated as hedging instrument [Member] Foreign currency forward contracts [Member]	Dec. 31, 2013 Derivatives not designated as hedging instrument [Member] Foreign currency forward contracts [Member]	Dec. 31, 2012 Derivatives not designated as hedging instrument [Member] Foreign currency forward contracts [Member]	Dec. 31, 2011 Derivatives not designated as hedging instrument [Member] Foreign currency forward contracts [Member]
Derivative instruments (Textual) [Abstract]
Length of time hedged in foreign currency contracts	3 years
Notional amount								$ 4,400	$ 3,600				$ 516	$ 200	$ 292	$ 4,400	$ 3,600	$ 4,000	$ 3,700	$ 3,500	$ 999	$ 629	$ 389
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					(51)
Amounts expected to be reclassified from accumulated other comprehensive income into earnings over the next 12 months - gain (loss)						(1)
Derivative lower range variable interest rate										1.10%	0.30%
Derivative higher range variable interest rate										2.00%	2.60%
Receipt from counterparties upon termination of interest rate swap contracts							397					397
Unrealized gain (loss) on the hedged debt		161	(20)	(182)
Offsetting unrealized gain (loss) on related interest rate swaps		$ (161)	$ 20	$ 182