Fair value measurement (Details) - USD ($)	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Assets:
Interest-bearing securities	$ 28,836,000,000		$ 41,169,000,000
Equity securities	200,000,000
Fair Value, Measurements, Recurring [Member]
Assets:
Equity securities	200,000,000		149,000,000
Derivatives:
Total assets	29,414,000,000		41,604,000,000
Derivatives:
Contingent consideration obligations in connection with business combinations	72,000,000		69,000,000
Total liabilities	699,000,000		554,000,000
Fair Value, Measurements, Recurring [Member] | Foreign currency contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	106,000,000		6,000,000
Derivatives:
Foreign currency and cross-currency swap contracts	65,000,000		204,000,000
Fair Value, Measurements, Recurring [Member] | Cross-currency swap contracts [Member]
Derivatives:
Foreign currency and cross-currency swap contracts	272,000,000		270,000,000
Derivatives:
Foreign currency and cross-currency swap contracts	296,000,000		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	266,000,000		61,000,000
Fair Value, Measurements, Recurring [Member] | U.S. Treasury securities [Member]
Assets:
Interest-bearing securities	3,391,000,000		8,242,000,000
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - U.S. [Member]
Assets:
Interest-bearing securities	128,000,000		223,000,000
Fair Value, Measurements, Recurring [Member] | Other government-related debt securities - Foreign and other [Member]
Assets:
Interest-bearing securities	1,390,000,000		2,422,000,000
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Financial [Member]
Assets:
Interest-bearing securities	3,968,000,000		10,072,000,000
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Industrial [Member]
Assets:
Interest-bearing securities	3,839,000,000		9,670,000,000
Fair Value, Measurements, Recurring [Member] | Corporate debt securities - Other [Member]
Assets:
Interest-bearing securities	676,000,000		1,390,000,000
Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed securities [Member]
Assets:
Interest-bearing securities	1,579,000,000		2,168,000,000
Fair Value, Measurements, Recurring [Member] | Other mortgage- and asset-backed securities [Member]
Assets:
Interest-bearing securities	652,000,000		2,297,000,000
Fair Value, Measurements, Recurring [Member] | Money market mutual funds [Member]
Assets:
Interest-bearing securities	7,341,000,000		3,245,000,000
Fair Value, Measurements, Recurring [Member] | Other short-term interest-bearing securities [Member]
Assets:
Interest-bearing securities	5,872,000,000		1,440,000,000
Fair Value, Measurements, Recurring [Member] | Quoted prices in active markets for identical assets (Level 1) [Member]
Assets:
Equity securities	200,000,000		149,000,000
Derivatives:
Total assets	10,932,000,000		11,636,000,000
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		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 securities [Member]
Assets:
Interest-bearing securities	3,391,000,000		8,242,000,000
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	7,341,000,000		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	18,482,000,000		29,968,000,000
Derivatives:
Contingent consideration obligations in connection with business combinations	0		0
Total liabilities	627,000,000		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	106,000,000		6,000,000
Derivatives:
Foreign currency and cross-currency swap contracts	65,000,000		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	272,000,000		270,000,000
Derivatives:
Foreign currency and cross-currency swap contracts	296,000,000		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	266,000,000		61,000,000
Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2) [Member] | U.S. Treasury securities [Member]
Assets:
Interest-bearing securities	0		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	128,000,000		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	1,390,000,000		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	3,968,000,000		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	3,839,000,000		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	676,000,000		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	1,579,000,000		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	652,000,000		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	5,872,000,000		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 in connection with business combinations	72,000,000	$ 110,000,000	69,000,000	$ 182,000,000	$ 184,000,000	$ 179,000,000
Total liabilities	72,000,000		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 securities [Member]
Assets:
Interest-bearing securities	0		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