Fair value measurement - (Fair Value of Financial Assets and Liabilities on Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets:
Interest-bearing securities	$ 8,234	$ 28,724
Equity securities	303	176
Derivatives:
Total assets	9,086	29,308
Derivatives:
Contingent consideration obligations	61	72
Total liabilities	407	648
Foreign currency contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	224	182
Derivatives:
Foreign currency and cross-currency swap contracts	31	26
Cross-currency swap contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	66	170
Derivatives:
Foreign currency and cross-currency swap contracts	315	401
Interest rate swap contracts [Member]
Derivatives:
Interest rate swap contracts	259	56
Derivatives:
Interest rate swap contracts	0	149
U.S. Treasury notes [Member]
Assets:
Interest-bearing securities	360	2,663
U.S. Treasury bills [Member]
Assets:
Interest-bearing securities	0	8,191
Other government-related debt securities - U.S. [Member]
Assets:
Interest-bearing securities	0	110
Other government-related debt securities - Foreign and other [Member]
Assets:
Interest-bearing securities	0	932
Corporate debt securities - Financial [Member]
Assets:
Interest-bearing securities	1,121	2,697
Corporate debt securities - Industrial [Member]
Assets:
Interest-bearing securities	834	2,504
Corporate debt securities - Other [Member]
Assets:
Interest-bearing securities	198	562
Residential mortgage-backed securities [Member]
Assets:
Interest-bearing securities	182	1,422
Other mortgage- and asset-backed securities [Member]
Assets:
Interest-bearing securities	0	469
Money market mutual funds [Member]
Assets:
Interest-bearing securities	5,250	5,659
Other short-term interest-bearing securities [Member]
Assets:
Interest-bearing securities	289	3,515
Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Equity securities	303	176
Derivatives:
Total assets	5,913	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
Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. Treasury notes [Member]
Assets:
Interest-bearing securities	360	2,663
Quoted prices in active markets for identical assets (Level 1) [Member] | U.S. Treasury bills [Member]
Assets:
Interest-bearing securities	0	8,191
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
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
Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate debt securities - Financial [Member]
Assets:
Interest-bearing securities	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate debt securities - Industrial [Member]
Assets:
Interest-bearing securities	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | Corporate debt securities - Other [Member]
Assets:
Interest-bearing securities	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | Residential mortgage-backed securities [Member]
Assets:
Interest-bearing securities	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Interest-bearing securities	0	0
Quoted prices in active markets for identical assets (Level 1) [Member] | Money market mutual funds [Member]
Assets:
Interest-bearing securities	5,250	5,659
Quoted prices in active markets for identical assets (Level 1) [Member] | Other short-term interest-bearing securities [Member]
Assets:
Interest-bearing securities	0	0
Significant other observable inputs (Level 2) [Member]
Assets:
Equity securities	0	0
Derivatives:
Total assets	3,173	12,619
Derivatives:
Contingent consideration obligations	0	0
Total liabilities	346	576
Significant other observable inputs (Level 2) [Member] | Foreign currency contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	224	182
Derivatives:
Foreign currency and cross-currency swap contracts	31	26
Significant other observable inputs (Level 2) [Member] | Cross-currency swap contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	66	170
Derivatives:
Foreign currency and cross-currency swap contracts	315	401
Significant other observable inputs (Level 2) [Member] | Interest rate swap contracts [Member]
Derivatives:
Interest rate swap contracts	259	56
Derivatives:
Interest rate swap contracts	0	149
Significant other observable inputs (Level 2) [Member] | U.S. Treasury notes [Member]
Assets:
Interest-bearing securities	0	0
Significant other observable inputs (Level 2) [Member] | U.S. Treasury bills [Member]
Assets:
Interest-bearing securities	0	0
Significant other observable inputs (Level 2) [Member] | Other government-related debt securities - U.S. [Member]
Assets:
Interest-bearing securities	0	110
Significant other observable inputs (Level 2) [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Interest-bearing securities	0	932
Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Financial [Member]
Assets:
Interest-bearing securities	1,121	2,697
Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Industrial [Member]
Assets:
Interest-bearing securities	834	2,504
Significant other observable inputs (Level 2) [Member] | Corporate debt securities - Other [Member]
Assets:
Interest-bearing securities	198	562
Significant other observable inputs (Level 2) [Member] | Residential mortgage-backed securities [Member]
Assets:
Interest-bearing securities	182	1,422
Significant other observable inputs (Level 2) [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Interest-bearing securities	0	469
Significant other observable inputs (Level 2) [Member] | Money market mutual funds [Member]
Assets:
Interest-bearing securities	0	0
Significant other observable inputs (Level 2) [Member] | Other short-term interest-bearing securities [Member]
Assets:
Interest-bearing securities	289	3,515
Significant unobservable inputs (Level 3) [Member]
Assets:
Equity securities	0	0
Derivatives:
Total assets		0
Derivatives:
Contingent consideration obligations	61	72
Total liabilities	61	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
Significant unobservable inputs (Level 3) [Member] | U.S. Treasury notes [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | U.S. Treasury bills [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | Other government-related debt securities - U.S. [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | Corporate debt securities - Financial [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | Corporate debt securities - Industrial [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | Corporate debt securities - Other [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | Residential mortgage-backed securities [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | Money market mutual funds [Member]
Assets:
Interest-bearing securities	0	0
Significant unobservable inputs (Level 3) [Member] | Other short-term interest-bearing securities [Member]
Assets:
Interest-bearing securities	$ 0	$ 0