Fair value measurements - Summary of assets and liabilities recorded at fair value (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	$ 34,301
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Available-for-sale Securities, Equity Securities	635	$ 428
Deferred compensation plan	116	84
Foreign currency derivative contracts	13	336
Fair Value Assets, total	35,065	30,711
Deferred compensation plan	116	84
Foreign currency derivative contracts	93	37
Contingent consideration	15	25
Fair Value Liabilities, total	224	146
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Available-for-sale Securities, Equity Securities	635	428
Deferred compensation plan	116	84
Foreign currency derivative contracts	0	0
Fair Value Assets, total	9,526	11,505
Deferred compensation plan	116	84
Foreign currency derivative contracts	0	0
Contingent consideration	0	0
Fair Value Liabilities, total	116	84
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Available-for-sale Securities, Equity Securities		0
Deferred compensation plan	0	0
Foreign currency derivative contracts	13	336
Fair Value Assets, total	25,539	19,206
Deferred compensation plan	0	0
Foreign currency derivative contracts	93	37
Contingent consideration	0	0
Fair Value Liabilities, total	93	37
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Available-for-sale Securities, Equity Securities	0	0
Deferred compensation plan	0	0
Foreign currency derivative contracts	0	0
Fair Value Assets, total	0	0
Deferred compensation plan	0	0
Foreign currency derivative contracts	0	0
Contingent consideration	15	25
Fair Value Liabilities, total	15	25
Corporate debt securities \| Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	14,747	12,603
Corporate debt securities \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Corporate debt securities \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	14,747	12,603
Corporate debt securities \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Certificates of deposit \| Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	5,131	943
Certificates of deposit \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Certificates of deposit \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	5,131	943
Certificates of deposit \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Money market funds \| Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	4,714	5,464
Money market funds \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	4,714	5,464
Money market funds \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Money market funds \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
U.S. treasury securities \| Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	4,061	5,529
U.S. treasury securities \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	4,061	5,529
U.S. treasury securities \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
U.S. treasury securities \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Residential mortgage and asset-backed securities \| Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	4,058	3,602
Residential mortgage and asset-backed securities \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Residential mortgage and asset-backed securities \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	4,058	3,602
Residential mortgage and asset-backed securities \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
U.S. government agencies securities \| Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	926	975
U.S. government agencies securities \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
U.S. government agencies securities \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	926	975
U.S. government agencies securities \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Non-U.S. government securities \| Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	664	720
Non-U.S. government securities \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Non-U.S. government securities \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	664	720
Non-U.S. government securities \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Municipal debt securities \| Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	27
Municipal debt securities \| Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	0
Municipal debt securities \| Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	0	27
Municipal debt securities \| Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis
Debt Securities, Fair Value	$ 0	$ 0

The fair value as of the balance sheet date of the liabilities related to the deferred compensation plan.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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- Definition

Amount of debt securities categorized neither as held-to-maturity nor trading.

+ References

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- Definition

Amount of equity securities categorized neither as held-to-maturity nor as trading.

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- Definition

Amount of liability recognized arising from contingent consideration in a business combination.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Fair value portion of asset contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward contracts, and swaps.

+ References

No definition available.

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Fair value portion of liability contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward (delivery or nondelivery) contracts, and swaps entered into.

+ References

No definition available.

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- Definition

Fair value of financial and nonfinancial obligations.

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- Definition

Fair value portion of other assets.

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No definition available.

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