Financial Instruments, Marketable securities, repurchase agreements, foreign currency rates, basis swaps and cross-currency swaps (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Marketable securities [Abstract]
Amount of marketable securities classified as cash and cash equivalents	$ 613		$ 613		$ 431
Repurchase agreements [Abstract]
Amount of repurchase agreements	$ 448		$ 448		350
Derivative [Line Items]
Foreign currency gain (loss)	gain of $3 million	loss of $1 million	gain of $7 million	loss of less than $1 million
Foreign currency rates [Member]
Derivative [Line Items]
Notional amounts value	$ 420		$ 420
Derivative, maturity date			October 2015 through December 2015
Basis swaps [Member] | Net-investment hedge [Member]
Derivative [Line Items]
Gain (loss) recognized related to the ineffectiveness of net investment hedging relationship	0		$ 0
Basis swaps [Member] | Net-investment hedge [Member] | Pay euro, expiration in 2016 [Member]
Derivative [Line Items]
Notional amounts value	$ 500		$ 500
Expiration date			2016
Average interest rate (in hundredths)	(0.22%)		(0.22%)
Fair value	$ 5		$ 5
Basis swaps [Member] | Net-investment hedge [Member] | Receive U.S. dollars, expiration in 2016 [Member]
Derivative [Line Items]
Expiration date			2016
Average interest rate (in hundredths)	0.33%		0.33%
Basis swaps [Member] | Net-investment hedge [Member] | Pay euro, expiration in 2017 [Member]
Derivative [Line Items]
Notional amounts value	$ 305		$ 305
Expiration date			2017
Average interest rate (in hundredths)	(0.26%)		(0.26%)
Fair value	$ 3		$ 3
Basis swaps [Member] | Net-investment hedge [Member] | Receive U.S. dollars, expiration in 2017 [Member]
Derivative [Line Items]
Expiration date			2017
Average interest rate (in hundredths)	0.33%		0.33%
Basis swaps [Member] | Net-investment hedge [Member] | Pay euro, expiration in 2018 [Member]
Derivative [Line Items]
Notional amounts value	$ 139		$ 139
Expiration date			2018
Average interest rate (in hundredths)	(0.27%)		(0.27%)
Fair value	$ 2		$ 2
Basis swaps [Member] | Net-investment hedge [Member] | Receive U.S. dollars, expiration in 2018 [Member]
Derivative [Line Items]
Expiration date			2018
Average interest rate (in hundredths)	0.33%		0.33%
Cross-currency swaps [Member] | Cash-flow hedge [Member]
Derivative [Line Items]
Gain (loss) recognized related to the ineffectiveness of cash flow hedging relationship	$ 0		$ 0
Cross-currency swaps [Member] | Cash-flow hedge [Member] | Pay euro, expiration in 2021 [Member]
Derivative [Line Items]
Notional amounts value	$ 1,000		$ 1,000		$ 1,000
Expiration date			2021		2021
Average interest rate (in hundredths)	4.55%		4.55%		4.55%
Fair value	$ 133		$ 133		$ 19
Cross-currency swaps [Member] | Cash-flow hedge [Member] | Receive U.S. dollars, expiration in 2021 [Member]
Derivative [Line Items]
Expiration date			2021		2021
Average interest rate (in hundredths)	6.00%		6.00%		6.00%
Cross-currency swaps [Member] | Cash-flow hedge [Member] | Pay euro, expiration in 2024 [Member]
Derivative [Line Items]
Notional amounts value	$ 1,000		$ 1,000		$ 1,000
Expiration date			2024		2024
Average interest rate (in hundredths)	4.37%		4.37%		4.37%
Fair value	$ 136		$ 136		$ 16
Cross-currency swaps [Member] | Cash-flow hedge [Member] | Receive U.S. dollars, expiration in 2024 [Member]
Derivative [Line Items]
Expiration date			2024		2024
Average interest rate (in hundredths)	5.75%		5.75%		5.75%
Cross-currency swaps [Member] | Cash-flow hedge [Member] | Pay euro, expiration in 2027 [Member]
Derivative [Line Items]
Notional amounts value	$ 300		$ 300
Expiration date			2027
Average interest rate (in hundredths)	3.69%		3.69%
Fair value	$ 7		$ 7
Cross-currency swaps [Member] | Cash-flow hedge [Member] | Receive U.S. dollars, expiration in 2027 [Member]
Derivative [Line Items]
Expiration date			2027
Average interest rate (in hundredths)	5.49%		5.49%