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Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Investments	$ 15,183	$ 20,179
Derivative assets	130	995
Liabilities
Contingent consideration	935	891	$ 590
Derivative liabilities	217	134
Commercial paper
Assets
Investments	159	4,330
Corporate notes and bonds
Assets
Investments	9,806	10,577
U.S. government and agency securities
Assets
Investments	2,042	2,232
Asset-backed securities
Assets
Investments	$ 1,542	1,376
Liabilities
Primary weighted-average lives of investment collateral (or less)	5 years
Mortgage-backed securities
Assets
Investments	$ 626	796
Foreign government bonds
Assets
Investments	733	519
Equity securities
Assets
Investments	275	349
Fair Value, Measurements, Recurring
Assets
Investments	14,531	19,242
Other assets	652	937
Derivative assets	130	995
Total assets	15,313	21,174
Liabilities
Contingent consideration	935	891
Derivative liabilities	217	134
Total liabilities	1,152	1,025
Fair Value, Measurements, Recurring | Purchased currency options
Assets
Derivative assets	80	644
Liabilities
Derivative liabilities	0	12
Fair Value, Measurements, Recurring | Foreign exchange contracts
Assets
Derivative assets	48	331
Liabilities
Derivative liabilities	162	93
Fair Value, Measurements, Recurring | Interest rate swap contracts
Assets
Derivative assets	2	20
Liabilities
Derivative liabilities	55	29
Fair Value, Measurements, Recurring | Commercial paper
Assets
Investments	159	4,330
Fair Value, Measurements, Recurring | Corporate notes and bonds
Assets
Investments	9,678	10,389
Other assets	128	188
Fair Value, Measurements, Recurring | U.S. government and agency securities
Assets
Investments	1,835	1,919
Other assets	207	313
Fair Value, Measurements, Recurring | Asset-backed securities
Assets
Investments	1,476	1,257
Other assets	66	119
Fair Value, Measurements, Recurring | Mortgage-backed securities
Assets
Investments	547	628
Other assets	79	168
Fair Value, Measurements, Recurring | Foreign government bonds
Assets
Investments	732	518
Other assets	1	1
Fair Value, Measurements, Recurring | Equity securities
Assets
Investments	104	201
Other assets	171	148
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Investments	172	230
Other assets	171	148
Derivative assets	0	0
Total assets	343	378
Liabilities
Contingent consideration	0	0
Derivative liabilities	0	0
Total liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Purchased currency options
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Foreign exchange contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Interest rate swap contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Commercial paper
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate notes and bonds
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | U.S. government and agency securities
Assets
Investments	68	29
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Asset-backed securities
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Mortgage-backed securities
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Foreign government bonds
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Equity securities
Assets
Investments	104	201
Other assets	171	148
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets
Investments	14,359	19,012
Other assets	481	789
Derivative assets	130	995
Total assets	14,970	20,796
Liabilities
Contingent consideration	0	0
Derivative liabilities	217	134
Total liabilities	217	134
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Purchased currency options
Assets
Derivative assets	80	644
Liabilities
Derivative liabilities	0	12
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign exchange contracts
Assets
Derivative assets	48	331
Liabilities
Derivative liabilities	162	93
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swap contracts
Assets
Derivative assets	2	20
Liabilities
Derivative liabilities	55	29
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial paper
Assets
Investments	159	4,330
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate notes and bonds
Assets
Investments	9,678	10,389
Other assets	128	188
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. government and agency securities
Assets
Investments	1,767	1,890
Other assets	207	313
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Asset-backed securities
Assets
Investments	1,476	1,257
Other assets	66	119
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Assets
Investments	547	628
Other assets	79	168
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign government bonds
Assets
Investments	732	518
Other assets	1	1
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Equity securities
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Assets
Investments	0	0
Other assets	0	0
Derivative assets	0	0
Total assets	0	0
Liabilities
Contingent consideration	935	891
Derivative liabilities	0	0
Total liabilities	935	891
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Purchased currency options
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign exchange contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Interest rate swap contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Commercial paper
Assets
Investments	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate notes and bonds
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. government and agency securities
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Asset-backed securities
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Mortgage-backed securities
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign government bonds
Assets
Investments	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Equity securities
Assets
Investments	0	0
Other assets	$ 0	$ 0

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