Fair value measurement (Details) - USD ($) $ in Millions | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2014 |
Assets: | | | | | | |
Total available-for-sale investments | $ 34,690 | | $ 31,112 | | | |
Fair Value, Measurements, Recurring [Member] | | | | | | |
Derivatives: | | | | | | |
Total assets | 35,041 | | 31,325 | | | |
Derivatives: | | | | | | |
Contingent consideration obligations in connection with business combinations | 171 | | 188 | | | |
Total liabilities | 658 | | 449 | | | |
Fair Value, Measurements, Recurring [Member] | Foreign currency contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 68 | | 142 | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 27 | | 8 | | | |
Fair Value, Measurements, Recurring [Member] | Cross currency swap contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 17 | | | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 456 | | 250 | | | |
Fair Value, Measurements, Recurring [Member] | Interest rate swap contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Interest rate contracts | 266 | | 71 | | | |
Derivatives: | | | | | | |
Interest rate swap contracts | | | 3 | | | |
Fair Value, Measurements, Recurring [Member] | Forward interest rate contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Interest rate swap contracts | 4 | | | | | |
Fair Value, Measurements, Recurring [Member] | U.S. Treasury securities [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 8,020 | | 4,274 | | | |
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - U.S. [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 347 | | 534 | | | |
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - Foreign and other [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 1,866 | | 1,739 | | | |
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Financial [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 8,238 | | 7,871 | | | |
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Industrial [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 8,473 | | 7,836 | | | |
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Other [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 1,018 | | 885 | | | |
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 1,738 | | 1,470 | | | |
Fair Value, Measurements, Recurring [Member] | Other mortgage- and asset-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 2,180 | | 2,469 | | | |
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 1,673 | | 3,370 | | | |
Fair Value, Measurements, Recurring [Member] | Other short-term interest-bearing securities [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 1,014 | | 528 | | | |
Fair Value, Measurements, Recurring [Member] | Equity securities [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 123 | | 136 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | | | | | | |
Derivatives: | | | | | | |
Total assets | 9,816 | | 7,780 | | | |
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 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Forward interest rate contracts [Member] | | | | | | |
Derivatives: | | | | | | |
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 | 8,020 | | 4,274 | | | |
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 | 1,673 | | 3,370 | | | |
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 | 123 | | 136 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | | | | | | |
Derivatives: | | | | | | |
Total assets | 25,225 | | 23,545 | | | |
Derivatives: | | | | | | |
Contingent consideration obligations in connection with business combinations | 0 | | 0 | | | |
Total liabilities | 487 | | 261 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Foreign currency contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 68 | | 142 | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 27 | | 8 | | | |
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 | 17 | | | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 456 | | 250 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Interest rate swap contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Interest rate contracts | 266 | | 71 | | | |
Derivatives: | | | | | | |
Interest rate swap contracts | | | 3 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Forward interest rate contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Interest rate swap contracts | 4 | | | | | |
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 | 347 | | 534 | | | |
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 | 1,866 | | 1,739 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Financial [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 8,238 | | 7,871 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Industrial [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 8,473 | | 7,836 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Other [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 1,018 | | 885 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential mortgage-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Total available-for-sale investments | 1,738 | | 1,470 | | | |
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 | 2,180 | | 2,469 | | | |
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 | 1,014 | | 528 | | | |
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 | 171 | $ 194 | 188 | $ 215 | $ 215 | $ 215 |
Total liabilities | 171 | | 188 | | | |
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 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Forward interest rate contracts [Member] | | | | | | |
Derivatives: | | | | | | |
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 | | | |