Financial Instruments - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Investments, debt securities	$ 7,261	$ 14,908
Publicly traded equity securities	456
Derivative assets	454	130
Liabilities
Contingent consideration	788	935	$ 891
Derivative liabilities	160	217
Commercial paper
Assets
Investments, debt securities	0	159
Corporate notes and bonds
Assets
Investments, debt securities	4,920	9,806
Asset-backed securities
Assets
Investments, debt securities	$ 1,275	1,542
Liabilities
Primary weighted-average lives of investment collateral (or less)	5 years
U.S. government and agency securities
Assets
Investments, debt securities	$ 892	2,042
Foreign government bonds
Assets
Investments, debt securities	166	733
Mortgage-backed securities
Assets
Investments, debt securities	8	626
Fair Value, Measurements, Recurring
Assets
Investments	7,132	14,531
Other assets	585	652
Derivative assets	454	130
Total assets	8,171	15,313
Liabilities
Contingent consideration	788	935
Derivative liabilities	160	217
Total liabilities	948	1,152
Fair Value, Measurements, Recurring | Interest rate swap contracts
Assets
Derivative assets	0	2
Liabilities
Derivative liabilities	81	55
Fair Value, Measurements, Recurring | Foreign exchange contracts
Assets
Derivative assets	241	48
Liabilities
Derivative liabilities	74	162
Fair Value, Measurements, Recurring | Purchased currency options
Assets
Derivative assets	213	80
Liabilities
Derivative liabilities	5	0
Fair Value, Measurements, Recurring | Commercial paper
Assets
Investments, debt securities	0	159
Fair Value, Measurements, Recurring | Corporate notes and bonds
Assets
Investments, debt securities	4,835	9,678
Other assets	85	128
Fair Value, Measurements, Recurring | Asset-backed securities
Assets
Investments, debt securities	1,253	1,476
Other assets	22	66
Fair Value, Measurements, Recurring | U.S. government and agency securities
Assets
Investments, debt securities	731	1,835
Other assets	161	207
Fair Value, Measurements, Recurring | Foreign government bonds
Assets
Investments, debt securities	166	732
Other assets	0	1
Fair Value, Measurements, Recurring | Mortgage-backed securities
Assets
Investments, debt securities	0	547
Other assets	8	79
Fair Value, Measurements, Recurring | Publicly traded equity securities
Assets
Publicly traded equity securities	147	104
Other assets	309	171
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1)
Assets
Investments	147	172
Other assets	364	171
Derivative assets	0	0
Total assets	511	343
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) | 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) | 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) | 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) | Commercial paper
Assets
Investments, debt securities	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate notes and bonds
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Asset-backed securities
Assets
Investments, debt securities	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, debt securities	0	68
Other assets	55	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Foreign government bonds
Assets
Investments, debt securities	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, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Quoted Prices In Active Markets for Identical Assets (Level 1) | Publicly traded equity securities
Assets
Publicly traded equity securities	147	104
Other assets	309	171
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Assets
Investments	6,985	14,359
Other assets	221	481
Derivative assets	454	130
Total assets	7,660	14,970
Liabilities
Contingent consideration	0	0
Derivative liabilities	160	217
Total liabilities	160	217
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swap contracts
Assets
Derivative assets	0	2
Liabilities
Derivative liabilities	81	55
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign exchange contracts
Assets
Derivative assets	241	48
Liabilities
Derivative liabilities	74	162
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Purchased currency options
Assets
Derivative assets	213	80
Liabilities
Derivative liabilities	5	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial paper
Assets
Investments, debt securities	0	159
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate notes and bonds
Assets
Investments, debt securities	4,835	9,678
Other assets	85	128
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Asset-backed securities
Assets
Investments, debt securities	1,253	1,476
Other assets	22	66
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. government and agency securities
Assets
Investments, debt securities	731	1,767
Other assets	106	207
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign government bonds
Assets
Investments, debt securities	166	732
Other assets	0	1
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Assets
Investments, debt securities	0	547
Other assets	8	79
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Publicly traded equity securities
Assets
Publicly traded equity securities	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	788	935
Derivative liabilities	0	0
Total liabilities	788	935
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) | Foreign exchange contracts
Assets
Derivative assets	0	0
Liabilities
Derivative liabilities	0	0
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) | Commercial paper
Assets
Investments, debt securities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate notes and bonds
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Asset-backed securities
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | U.S. government and agency securities
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Foreign government bonds
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Mortgage-backed securities
Assets
Investments, debt securities	0	0
Other assets	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Publicly traded equity securities
Assets
Publicly traded equity securities	0	0
Other assets	$ 0	$ 0