Fair value measurement (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets:
Total available-for-sale investments	$ 24,935	$ 20,003
Fair Value, Measurements, Recurring [Member]
Derivative Assets:
Interest rate swap contracts		377
Total assets	25,034	20,552
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	195	190
Total liabilities	277	264
Fair Value, Measurements, Recurring [Member] | Foreign currency contracts [Member]
Derivative Assets:
Foreign currency contracts	87	172
Derivative Liabilities:
Foreign currency contracts	55	48
Fair Value, Measurements, Recurring [Member] | Cross currency swap contracts [Member]
Derivative Assets:
Foreign currency contracts	12
Derivative Liabilities:
Foreign currency contracts	27	26
Fair Value, Measurements, Recurring [Member] | U.S. Treasury securities [Member]
Assets:
Total available-for-sale investments	3,960	3,946
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - Obligations of U.S. government agencies and FDIC-guaranteed bank debt [Member]
Assets:
Total available-for-sale investments	1,198	1,571
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Total available-for-sale investments	1,712	450
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	3,256	2,508
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	4,318	3,146
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	432	289
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities [Member]
Assets:
Total available-for-sale investments	1,836	518
Fair Value, Measurements, Recurring [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Total available-for-sale investments	2,066	1,267
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member]
Assets:
Total available-for-sale investments	4,000	6,266
Fair Value, Measurements, Recurring [Member] | Other short-term interest bearing securities [Member]
Assets:
Total available-for-sale investments	2,105
Fair Value, Measurements, Recurring [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	52	42
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Derivative Assets:
Interest rate swap contracts		0
Total assets	8,012	10,254
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
Derivative Liabilities:
Foreign currency 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	3,960	3,946
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Other government-related debt securities - Obligations of U.S. government agencies and FDIC-guaranteed bank debt [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	4,000	6,266
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
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	52	42
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member]
Derivative Assets:
Interest rate swap contracts		377
Total assets	17,022	10,298
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	0	0
Total liabilities	82	74
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Foreign currency contracts [Member]
Derivative Assets:
Foreign currency contracts	87	172
Derivative Liabilities:
Foreign currency contracts	55	48
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Cross currency swap contracts [Member]
Derivative Assets:
Foreign currency contracts	12
Derivative Liabilities:
Foreign currency contracts	27	26
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 - Obligations of U.S. government agencies and FDIC-guaranteed bank debt [Member]
Assets:
Total available-for-sale investments	1,198	1,571
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	1,712	450
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	3,256	2,508
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	4,318	3,146
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	432	289
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential mortgage-backed securities [Member]
Assets:
Total available-for-sale investments	1,836	518
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	2,066	1,267
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	2,105
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:
Interest rate swap contracts		0
Total assets	0	0
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	195	190
Total liabilities	195	190
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
Derivative Liabilities:
Foreign currency 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 - Obligations of U.S. government agencies and FDIC-guaranteed bank debt [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
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	$ 0	$ 0