Fair value measurement (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets:
Total available-for-sale investments	$ 22,363	$ 23,745
Fair Value, Measurements, Recurring [Member]
Derivative Assets:
Total assets	22,609	23,856
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	595	221
Total liabilities	867	286
Fair Value, Measurements, Recurring [Member] | Foreign currency contracts [Member]
Derivative Assets:
Foreign currency contracts	53	46
Derivative Liabilities:
Foreign currency contracts	107	59
Fair Value, Measurements, Recurring [Member] | Cross currency swap contracts [Member]
Derivative Assets:
Foreign currency contracts	193	65
Derivative Liabilities:
Foreign currency contracts	4	6
Fair Value, Measurements, Recurring [Member] | Interest rate swap contracts [Member]
Derivative Liabilities:
Interest rate swap contracts	161
Fair Value, Measurements, Recurring [Member] | U.S. Treasury securities [Member]
Assets:
Total available-for-sale investments	4,730	4,458
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - U.S. [Member]
Assets:
Total available-for-sale investments	1,079	1,030
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Total available-for-sale investments	1,546	1,608
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	3,676	3,361
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	3,760	4,380
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	390	452
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities [Member]
Assets:
Total available-for-sale investments	1,460	1,829
Fair Value, Measurements, Recurring [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Total available-for-sale investments	1,511	1,767
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member]
Assets:
Total available-for-sale investments	3,366	2,620
Fair Value, Measurements, Recurring [Member] | Other short-term interest-bearing securities [Member]
Assets:
Total available-for-sale investments	750	2,186
Fair Value, Measurements, Recurring [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	95	54
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Derivative Assets:
Total assets	8,191	7,132
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	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]
Derivative Assets:
Foreign currency contracts	0	0
Derivative Liabilities:
Foreign currency contracts	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Cross currency swap contracts [Member]
Derivative Assets:
Foreign currency contracts	0	0
Derivative Liabilities:
Foreign currency contracts	0	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Interest rate swap contracts [Member]
Derivative Liabilities:
Interest rate swap contracts	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	4,730	4,458
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	3,366	2,620
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	95	54
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member]
Derivative Assets:
Total assets	14,418	16,724
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	0	0
Total liabilities	272	65
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Foreign currency contracts [Member]
Derivative Assets:
Foreign currency contracts	53	46
Derivative Liabilities:
Foreign currency contracts	107	59
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Cross currency swap contracts [Member]
Derivative Assets:
Foreign currency contracts	193	65
Derivative Liabilities:
Foreign currency contracts	4	6
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Interest rate swap contracts [Member]
Derivative Liabilities:
Interest rate swap contracts	161
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	1,079	1,030
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	1,546	1,608
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	3,676	3,361
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	3,760	4,380
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	390	452
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential mortgage-backed securities [Member]
Assets:
Total available-for-sale investments	1,460	1,829
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	1,511	1,767
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	750	2,186
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]
Derivative Assets:
Total assets		0
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	595	221	190
Total liabilities	595	221
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Foreign currency contracts [Member]
Derivative Assets:
Foreign currency contracts	0	0
Derivative Liabilities:
Foreign currency contracts	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Cross currency swap contracts [Member]
Derivative Assets:
Foreign currency contracts	0	0
Derivative Liabilities:
Foreign currency contracts	0	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Interest rate swap contracts [Member]
Derivative Liabilities:
Interest rate swap contracts	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