Fair value measurement (Details) - USD ($) | Sep. 30, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Dec. 31, 2016 |
Assets: | | | | | | |
Interest-bearing securities | $ 29,418,000,000 | | $ 41,169,000,000 | | | |
Equity securities | 217,000,000 | | | | | |
Derivatives: | | | | | | |
Contingent consideration obligations | | | 0 | | | $ 116,000,000 |
Fair Value, Measurements, Recurring [Member] | | | | | | |
Assets: | | | | | | |
Equity securities | 217,000,000 | | 149,000,000 | | | |
Derivatives: | | | | | | |
Total assets | 30,017,000,000 | | 41,604,000,000 | | | |
Derivatives: | | | | | | |
Contingent consideration obligations | 66,000,000 | | 69,000,000 | | | |
Total liabilities | 731,000,000 | | 554,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Foreign currency contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 121,000,000 | | 6,000,000 | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 49,000,000 | | 204,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Cross-currency swap contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 261,000,000 | | 270,000,000 | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 306,000,000 | | 220,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Interest rate swap contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Interest rate contracts | | | 10,000,000 | | | |
Derivatives: | | | | | | |
Interest rate swap contracts | 310,000,000 | | 61,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | U.S. Treasury notes [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 2,626,000,000 | | 8,242,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | U.S. Treasury bills [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 5,376,000,000 | | | | | |
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - U.S. [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 109,000,000 | | 223,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - Foreign and other [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 1,008,000,000 | | 2,422,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Financial [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 2,697,000,000 | | 10,072,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Industrial [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 2,578,000,000 | | 9,670,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Other [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 573,000,000 | | 1,390,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 1,462,000,000 | | 2,168,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Other mortgage- and asset-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 473,000,000 | | 2,297,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 8,955,000,000 | | 3,245,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Other short-term interest-bearing securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 3,561,000,000 | | 1,440,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | | | | | | |
Assets: | | | | | | |
Equity securities | 217,000,000 | | 149,000,000 | | | |
Derivatives: | | | | | | |
Total assets | 17,174,000,000 | | 11,636,000,000 | | | |
Derivatives: | | | | | | |
Contingent consideration obligations | 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 | | 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 | | | |
Derivatives: | | | | | | |
Interest rate swap contracts | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. Treasury notes [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 2,626,000,000 | | 8,242,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. Treasury bills [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 5,376,000,000 | | | | | |
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: | | | | | | |
Interest-bearing securities | 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: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate debt securities - Financial [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate debt securities - Industrial [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate debt securities - Other [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Residential mortgage-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 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: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Money market mutual funds [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 8,955,000,000 | | 3,245,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member] | Other short-term interest-bearing securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | | | | | | |
Assets: | | | | | | |
Equity securities | 0 | | 0 | | | |
Derivatives: | | | | | | |
Total assets | 12,843,000,000 | | 29,968,000,000 | | | |
Derivatives: | | | | | | |
Contingent consideration obligations | 0 | | 0 | | | |
Total liabilities | 665,000,000 | | 485,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Foreign currency contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 121,000,000 | | 6,000,000 | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 49,000,000 | | 204,000,000 | | | |
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 | 261,000,000 | | 270,000,000 | | | |
Derivatives: | | | | | | |
Foreign currency and cross-currency swap contracts | 306,000,000 | | 220,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Interest rate swap contracts [Member] | | | | | | |
Derivatives: | | | | | | |
Interest rate contracts | | | 10,000,000 | | | |
Derivatives: | | | | | | |
Interest rate swap contracts | 310,000,000 | | 61,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | U.S. Treasury notes [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | U.S. Treasury bills [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other government-related debt securities - U.S. [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 109,000,000 | | 223,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other government-related debt securities - Foreign and other [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 1,008,000,000 | | 2,422,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Financial [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 2,697,000,000 | | 10,072,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Industrial [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 2,578,000,000 | | 9,670,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Other [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 573,000,000 | | 1,390,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Residential mortgage-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 1,462,000,000 | | 2,168,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other mortgage- and asset-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 473,000,000 | | 2,297,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Money market mutual funds [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | Other short-term interest-bearing securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 3,561,000,000 | | 1,440,000,000 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | | | | | | |
Assets: | | | | | | |
Equity securities | 0 | | 0 | | | |
Derivatives: | | | | | | |
Total assets | 0 | | 0 | | | |
Derivatives: | | | | | | |
Contingent consideration obligations | 66,000,000 | $ 72,000,000 | 69,000,000 | $ 68,000,000 | $ 182,000,000 | $ 179,000,000 |
Total liabilities | 66,000,000 | | 69,000,000 | | | |
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 | | 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 | | | |
Derivatives: | | | | | | |
Interest rate swap contracts | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | U.S. Treasury notes [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | U.S. Treasury bills [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other government-related debt securities - U.S. [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other government-related debt securities - Foreign and other [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Corporate debt securities - Financial [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Corporate debt securities - Industrial [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Corporate debt securities - Other [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Residential mortgage-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other mortgage- and asset-backed securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Money market mutual funds [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | 0 | | 0 | | | |
Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3) [Member] | Other short-term interest-bearing securities [Member] | | | | | | |
Assets: | | | | | | |
Interest-bearing securities | $ 0 | | $ 0 | | | |