Fair Value Measurements - Summary of assets and liabilities measured at fair value (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Assets:
Estimated fair value	$ 40,054	$ 30,291
Fair Value, Measurements, Recurring \| Level 1
Assets:
Equity securities	683	428
Foreign currency derivative contracts	0	0
Deferred compensation plan	110	84
Total	13,943	11,505
Liabilities:
Deferred compensation plan	110	84
Foreign currency derivative contracts	0	0
Contingent consideration	0	0
Total	110	84
Fair Value, Measurements, Recurring \| Level 1 \| Corporate debt securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 1 \| U.S. treasury securities
Assets:
Estimated fair value	4,125	5,529
Fair Value, Measurements, Recurring \| Level 1 \| Money market funds
Assets:
Estimated fair value	9,025	5,464
Fair Value, Measurements, Recurring \| Level 1 \| Residential mortgage and asset-backed securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 1 \| U.S. government agencies securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Certificates of deposit
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Non-U.S. government securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Municipal debt securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 2
Assets:
Equity securities	0	0
Foreign currency derivative contracts	30	336
Deferred compensation plan	0	0
Total	26,251	19,206
Liabilities:
Deferred compensation plan	0	0
Foreign currency derivative contracts	101	37
Contingent consideration	0	0
Total	101	37
Fair Value, Measurements, Recurring \| Level 2 \| Corporate debt securities
Assets:
Estimated fair value	14,845	12,603
Fair Value, Measurements, Recurring \| Level 2 \| U.S. treasury securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 2 \| Money market funds
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 2 \| Residential mortgage and asset-backed securities
Assets:
Estimated fair value	4,213	3,602
Fair Value, Measurements, Recurring \| Level 2 \| U.S. government agencies securities
Assets:
Estimated fair value	958	975
Fair Value, Measurements, Recurring \| Level 2 \| Certificates of deposit
Assets:
Estimated fair value	5,511	943
Fair Value, Measurements, Recurring \| Level 2 \| Non-U.S. government securities
Assets:
Estimated fair value	684	720
Fair Value, Measurements, Recurring \| Level 2 \| Municipal debt securities
Assets:
Estimated fair value	10	27
Fair Value, Measurements, Recurring \| Level 3
Assets:
Equity securities	0	0
Foreign currency derivative contracts	0	0
Deferred compensation plan	0	0
Total	0	0
Liabilities:
Deferred compensation plan	0	0
Foreign currency derivative contracts	0	0
Contingent consideration	16	25
Total	16	25
Fair Value, Measurements, Recurring \| Level 3 \| Corporate debt securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 3 \| U.S. treasury securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Money market funds
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Residential mortgage and asset-backed securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 3 \| U.S. government agencies securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Certificates of deposit
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Non-U.S. government securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Municipal debt securities
Assets:
Estimated fair value	0	0
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement
Assets:
Equity securities	683	428
Foreign currency derivative contracts	30	336
Deferred compensation plan	110	84
Total	40,194	30,711
Liabilities:
Deferred compensation plan	110	84
Foreign currency derivative contracts	101	37
Contingent consideration	16	25
Total	227	146
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement \| Corporate debt securities
Assets:
Estimated fair value	14,845	12,603
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement \| U.S. treasury securities
Assets:
Estimated fair value	4,125	5,529
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement \| Money market funds
Assets:
Estimated fair value	9,025	5,464
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement \| Residential mortgage and asset-backed securities
Assets:
Estimated fair value	4,213	3,602
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement \| U.S. government agencies securities
Assets:
Estimated fair value	958	975
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement \| Certificates of deposit
Assets:
Estimated fair value	5,511	943
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement \| Non-U.S. government securities
Assets:
Estimated fair value	684	720
Fair Value, Measurements, Recurring \| Estimate of Fair Value Measurement \| Municipal debt securities
Assets:
Estimated fair value	$ 10	$ 27

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

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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

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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.

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Fair value of financial and nonfinancial obligations.

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