Stock-based compensation (Details 3) (Stock Options [Member], USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2013
Stock Options [Member]
Stock Options [Roll Forward]
Stock options unexercised, beginning balance (in shares)	12.3
Stock options, granted (in shares)	0.1
Stock options, exercised (in shares)	(4.7)
Stock options, expired/forfeited (in shares)	(0.3)
Stock options unexercised, ending balance (in shares)	7.4
Stock Options, Weighted Average Exercise Price [Roll Forward]
Weighted-average exercise price, unexercised beginning balance (in usd per share)	$ 56.09
Weighted-average exercise price, granted (in usd per share)	$ 85.59
Weighted-average exercise price, exercised (in usd per share)	$ 58.05
Weighted-average exercise price, expired/forfeited (in usd per share)	$ 56.93
Weighted-average exercise price, unexercised ending balance (in usd per share)	$ 54.91
Stock options information [Abstract]
Vested or expected to vest (in shares)	7.3
Exercisable (in shares)	4.8
Weighted-average exercise price, vested or expected to vest (in usd per share)	$ 54.91
Weighted-average exercise price, exercisable (in usd per share)	$ 53.95
Weighted-average remaining contractual life (years), unexercised	4 years 9 months 18 days
Weighted-average remaining contractual life (years), vested or expected to vest	4 years 9 months 18 days
Weighted-average remaining contractual life (years), exercisable	3 years 8 months 12 days
Aggregate intrinsic value, unexercised	$ 436
Aggregate intrinsic value, vested or expected to vest	434
Aggregate intrinsic value, exercisable	$ 291

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Net number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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