Fair value measurement (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets:
Total available-for-sale investments	$ 20,003	$ 17,325
Fair Value, Measurements, Recurring [Member]
Derivative Assets:
Interest rate swap contracts	377	195
Total assets	20,552	17,674
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	190
Total liabilities	264	103
Fair Value, Measurements, Recurring [Member] | Foreign currency contracts [Member]
Derivative Assets:
Foreign currency contracts	172	154
Derivative Liabilities:
Foreign currency contracts	48	103
Fair Value, Measurements, Recurring [Member] | Cross currency swap contracts [Member]
Derivative Liabilities:
Foreign currency contracts	26
Fair Value, Measurements, Recurring [Member] | US Treasury securities [Member]
Assets:
Total available-for-sale investments	3,946	5,080
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	1,571	2,208
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Total available-for-sale investments	450	852
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	2,508	2,296
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	3,146	2,507
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	289	316
Fair Value, Measurements, Recurring [Member] | Mortgage- and asset-backed securities [Member]
Assets:
Total available-for-sale investments	1,785	841
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member]
Assets:
Total available-for-sale investments	6,266	3,030
Fair Value, Measurements, Recurring [Member] | Other short-term interest-bearing securities [Member]
Assets:
Total available-for-sale investments		147
Fair Value, Measurements, Recurring [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	42	48
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Derivative Assets:
Interest rate swap contracts	0	0
Total assets	10,254	8,158
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	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 Liabilities:
Foreign currency contracts	0
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | US Treasury securities [Member]
Assets:
Total available-for-sale investments	3,946	5,080
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] | 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	6,266	3,030
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	42	48
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member]
Derivative Assets:
Interest rate swap contracts	377	195
Total assets	10,298	9,516
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	0
Total liabilities	74	103
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Foreign currency contracts [Member]
Derivative Assets:
Foreign currency contracts	172	154
Derivative Liabilities:
Foreign currency contracts	48	103
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Cross currency swap contracts [Member]
Derivative Liabilities:
Foreign currency contracts	26
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | US 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	1,571	2,208
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	450	852
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	2,508	2,296
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	3,146	2,507
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	289	316
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Mortgage- and asset-backed securities [Member]
Assets:
Total available-for-sale investments	1,785	841
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		147
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	0
Total assets	0	0
Derivative Liabilities:
Contingent consideration obligations in connection with a business combination	190
Total liabilities	190	0
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 Liabilities:
Foreign currency contracts	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | US 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] | 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