Fair value measurement (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets:
Interest-bearing securities	$ 25,652	$ 28,724
Equity securities	246	176
Derivatives:
Total assets	26,373	29,308
Derivatives:
Contingent consideration obligations	66	72
Total liabilities	557	648
Foreign currency contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	238	182
Derivatives:
Foreign currency and cross-currency swap contracts	8	26
Cross-currency swap contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	143	170
Derivatives:
Foreign currency and cross-currency swap contracts	429	401
Interest rate swap contracts [Member]
Derivatives:
Interest rate swap contracts	94	56
Derivatives:
Interest rate swap contracts	54	149
Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Equity securities	246	176
Derivatives:
Total assets	10,778	16,689
Derivatives:
Contingent consideration obligations	0	0
Total liabilities	0	0
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
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
Quoted prices in active markets for identical assets (Level 1) [Member] | Interest rate swap contracts [Member]
Derivatives:
Interest rate swap contracts	0	0
Derivatives:
Interest rate swap contracts	0	0
Significant other observable inputs (Level 2) [Member]
Assets:
Equity securities	0	0
Derivatives:
Total assets	15,595	12,619
Derivatives:
Contingent consideration obligations	0	0
Total liabilities	491	576
Significant other observable inputs (Level 2) [Member] | Foreign currency contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	238	182
Derivatives:
Foreign currency and cross-currency swap contracts	8	26
Significant other observable inputs (Level 2) [Member] | Cross-currency swap contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	143	170
Derivatives:
Foreign currency and cross-currency swap contracts	429	401
Significant other observable inputs (Level 2) [Member] | Interest rate swap contracts [Member]
Derivatives:
Interest rate swap contracts	94	56
Derivatives:
Interest rate swap contracts	54	149
Significant unobservable inputs (Level 3) [Member]
Assets:
Equity securities	0	0
Derivatives:
Total assets	0	0
Derivatives:
Contingent consideration obligations	66	72
Total liabilities	66	72
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
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
Significant unobservable inputs (Level 3) [Member] | Interest rate swap contracts [Member]
Derivatives:
Interest rate swap contracts	0	0
Derivatives:
Interest rate swap contracts	0	0
U.S. Treasury notes [Member]
Assets:
Interest-bearing securities	2,682	2,663
U.S. Treasury notes [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	2,682	2,663
U.S. Treasury notes [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	0	0
U.S. Treasury notes [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
U.S. Treasury bills [Member]
Assets:
Interest-bearing securities	3,475	8,191
U.S. Treasury bills [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	3,475	8,191
U.S. Treasury bills [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	0	0
U.S. Treasury bills [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
Other government-related debt securities - U.S. [Member]
Assets:
Interest-bearing securities	111	110
Other government-related debt securities - U.S. [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	0	0
Other government-related debt securities - U.S. [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	111	110
Other government-related debt securities - U.S. [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
Other government-related debt securities - Foreign and other [Member]
Assets:
Interest-bearing securities	958	932
Other government-related debt securities - Foreign and other [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	0	0
Other government-related debt securities - Foreign and other [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	958	932
Other government-related debt securities - Foreign and other [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
Corporate debt securities - Financial [Member]
Assets:
Interest-bearing securities	2,750	2,697
Corporate debt securities - Financial [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	0	0
Corporate debt securities - Financial [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	2,750	2,697
Corporate debt securities - Financial [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
Corporate debt securities - Industrial [Member]
Assets:
Interest-bearing securities	2,458	2,504
Corporate debt securities - Industrial [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	0	0
Corporate debt securities - Industrial [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	2,458	2,504
Corporate debt securities - Industrial [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
Corporate debt securities - Other [Member]
Assets:
Interest-bearing securities	566	562
Corporate debt securities - Other [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	0	0
Corporate debt securities - Other [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	566	562
Corporate debt securities - Other [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
Residential mortgage-backed securities [Member]
Assets:
Interest-bearing securities	1,382	1,422
Residential mortgage-backed securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	0	0
Residential mortgage-backed securities [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	1,382	1,422
Residential mortgage-backed securities [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
Other mortgage- and asset-backed securities [Member]
Assets:
Interest-bearing securities	467	469
Other mortgage- and asset-backed securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	0	0
Other mortgage- and asset-backed securities [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	467	469
Other mortgage- and asset-backed securities [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
Money market mutual funds [Member]
Assets:
Interest-bearing securities	4,375	5,659
Money market mutual funds [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	4,375	5,659
Money market mutual funds [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	0	0
Money market mutual funds [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	0	0
Other short-term interest-bearing securities [Member]
Assets:
Interest-bearing securities	6,428	3,515
Other short-term interest-bearing securities [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Interest-bearing securities	0	0
Other short-term interest-bearing securities [Member] | Significant other observable inputs (Level 2) [Member]
Assets:
Interest-bearing securities	6,428	3,515
Other short-term interest-bearing securities [Member] | Significant unobservable inputs (Level 3) [Member]
Assets:
Interest-bearing securities	$ 0	$ 0