Stock-based compensation - Employee stock purchase plan (Details) (TI employees 2005 stock purchase plan, USD $)	12 Months Ended
Dec. 31, 2014
TI employees 2005 stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, Beginning balance (in shares)	485,408
Granted (in shares)	1,673,479
Exercised (in shares)	(1,784,184)
Options outstanding, Ending balance (in shares)	374,703
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average exercise price, Outstanding, Beginning of period (in dollars per share)	$ 36.64
Weighted-average exercise price, Granted (in dollars per share)	$ 41.60
Weighted-average exercise price, Exercised (in dollars per share)	$ 39.44
Weighted-average exercise price, Outstanding, End of period (in dollars per share)	$ 45.46

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(1)

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

+ References

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

+ References

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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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