Fair value measurement (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Assets:
Total available-for-sale investments	$ 19,037	$ 17,325
Fair Value, Measurements, Recurring [Member]
Derivatives Assets:
Foreign currency contracts	50	154
Interest rate swap contracts	232	195
Total assets	19,319	17,674
Derivatives Liabilities:
Foreign currency contracts	170	103
Contingent consideration obligations in connection with a business combination	192
Total liabilities	362	103
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Derivatives Assets:
Foreign currency contracts	0	0
Interest rate swap contracts	0	0
Total assets	8,631	8,158
Derivatives Liabilities:
Foreign currency contracts	0	0
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] | US Treasury securities [Member]
Assets:
Total available-for-sale investments	2,907	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	5,677	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	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	47	48
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member]
Derivatives Assets:
Foreign currency contracts	50	154
Interest rate swap contracts	232	195
Total assets	10,688	9,516
Derivatives Liabilities:
Foreign currency contracts	170	103
Contingent consideration obligations in connection with a business combination	0
Total liabilities	170	103
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	1,559	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	812	852
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	2,944	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	3,036	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	354	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	1,544	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	157	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]
Derivatives Assets:
Foreign currency contracts	0	0
Interest rate swap contracts	0	0
Total assets	0	0
Derivatives Liabilities:
Foreign currency contracts	0	0
Contingent consideration obligations in connection with a business combination	192
Total liabilities	192	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	0
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	0	0
Fair Value, Measurements, Recurring [Member] | US Treasury securities [Member]
Assets:
Total available-for-sale investments	2,907	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	1,559	2,208
Fair Value, Measurements, Recurring [Member] | Other government related debt securities - Foreign and other [Member]
Assets:
Total available-for-sale investments	812	852
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Financial [Member]
Assets:
Total available-for-sale investments	2,944	2,296
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Industrial [Member]
Assets:
Total available-for-sale investments	3,036	2,507
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Other [Member]
Assets:
Total available-for-sale investments	354	316
Fair Value, Measurements, Recurring [Member] | Mortgage and asset backed securities [Member]
Assets:
Total available-for-sale investments	1,544	841
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member]
Assets:
Total available-for-sale investments	5,677	3,030
Fair Value, Measurements, Recurring [Member] | Other short-term interest bearing securities [Member]
Assets:
Total available-for-sale investments	157	147
Fair Value, Measurements, Recurring [Member] | Equity securities [Member]
Assets:
Total available-for-sale investments	$ 47	$ 48