Fair value measurement (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Assets:
Total available-for-sale investments	$ 38,113	$ 37,781
Fair Value, Measurements, Recurring [Member]
Derivatives:
Total assets	38,311	38,025
Derivatives:
Contingent consideration obligations in connection with business combinations	184	179
Total liabilities	695	713
Fair Value, Measurements, Recurring [Member] | Foreign currency contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	148	203
Derivatives:
Foreign currency and cross-currency swap contracts	15	4
Fair Value, Measurements, Recurring [Member] | Cross currency swap contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	20
Derivatives:
Foreign currency and cross-currency swap contracts	481	523
Fair Value, Measurements, Recurring [Member] | Interest rate swap contracts [Member]
Derivatives:
Interest rate contracts	30	41
Derivatives:
Interest rate swap contracts	15	7
Fair Value, Measurements, Recurring [Member] | U.S. Treasury securities [Member]
Assets:
Total available-for-sale investments	6,889	6,614
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - U.S. [Member]
Assets:
Total available-for-sale investments	239	299
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Total available-for-sale investments	1,826	1,759
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	8,564	8,460
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	8,791	8,789
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	1,112	1,077
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities [Member]
Assets:
Total available-for-sale investments	1,740	1,940
Fair Value, Measurements, Recurring [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Total available-for-sale investments	1,801	1,719
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member]
Assets:
Total available-for-sale investments	2,891	2,782
Fair Value, Measurements, Recurring [Member] | Other short-term interest-bearing securities [Member]
Assets:
Total available-for-sale investments	4,080	4,188
Fair Value, Measurements, Recurring [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	180	154
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Derivatives:
Total assets	9,960	9,550
Derivatives:
Contingent consideration obligations in connection with business combinations	0	0
Total liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Foreign currency contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	0	0
Derivatives:
Foreign currency and cross-currency swap contracts	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Cross currency swap contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	0
Derivatives:
Foreign currency and cross-currency swap contracts	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Interest rate swap contracts [Member]
Derivatives:
Interest rate contracts	0	0
Derivatives:
Interest rate swap contracts	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. Treasury securities [Member]
Assets:
Total available-for-sale investments	6,889	6,614
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Other government-related debt securities - U.S. [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Residential mortgage-backed securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Money market mutual funds [Member]
Assets:
Total available-for-sale investments	2,891	2,782
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Other short-term interest-bearing securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	180	154
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member]
Derivatives:
Total assets	28,351	28,475
Derivatives:
Contingent consideration obligations in connection with business combinations	0	0
Total liabilities	511	534
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Foreign currency contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	148	203
Derivatives:
Foreign currency and cross-currency swap contracts	15	4
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Cross currency swap contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	20
Derivatives:
Foreign currency and cross-currency swap contracts	481	523
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Interest rate swap contracts [Member]
Derivatives:
Interest rate contracts	30	41
Derivatives:
Interest rate swap contracts	15	7
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | U.S. Treasury securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other government-related debt securities - U.S. [Member]
Assets:
Total available-for-sale investments	239	299
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Total available-for-sale investments	1,826	1,759
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	8,564	8,460
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	8,791	8,789
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	1,112	1,077
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential mortgage-backed securities [Member]
Assets:
Total available-for-sale investments	1,740	1,940
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Total available-for-sale investments	1,801	1,719
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Money market mutual funds [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other short-term interest-bearing securities [Member]
Assets:
Total available-for-sale investments	4,080	4,188
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member]
Derivatives:
Total assets	0	0
Derivatives:
Contingent consideration obligations in connection with business combinations	184	179	$ 194	$ 188
Total liabilities	184	179
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Foreign currency contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	0	0
Derivatives:
Foreign currency and cross-currency swap contracts	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Cross currency swap contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	0
Derivatives:
Foreign currency and cross-currency swap contracts	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Interest rate swap contracts [Member]
Derivatives:
Interest rate contracts	0	0
Derivatives:
Interest rate swap contracts	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | U.S. Treasury securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other government-related debt securities - U.S. [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Residential mortgage-backed securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Money market mutual funds [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other short-term interest-bearing securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	$ 0	$ 0