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Financial Instruments - Narrative (Details)	12 Months Ended
Financial Instruments - Narrative (Details)	Dec. 31, 2018 USD ($) interest_rate_swap	Dec. 31, 2017 USD ($)	May 31, 2018 USD ($) interest_rate_swap
Derivative [Line Items]
Number of interest rate swaps held \| interest_rate_swap	19
Notional amount of derivative	$ 29,742,000,000	$ 25,595,000,000
Pre tax net unrealized gain (loss) on derivatives maturing within next 12 months estimated to be reclassified from AOCI to sales	186,000,000
Equity investments without readily determinable fair values	568,000,000
Unrealized gains based on favorable observable price changes	167,000,000
Unrealized loss related to unfavorable observable price changes	26,000,000
Available-for-sale debt securities included in Short-term investments	894,000,000
Available-for-sale debt securities maturing within five years	5,800,000,000
Cash and cash equivalents	7,965,000,000	6,092,000,000
Payments of contingent consideration	244,000,000	100,000,000
Fair value of loans payable and long-term debt, including current portion	25,600,000,000	25,600,000,000
Carrying value of loans payable and long-term debt, including current portion	25,100,000,000	24,400,000,000
Cash collateral received from counterparties	$ 107,000,000	3,000,000
Customer Concentration Risk \| Accounts Receivable \| McKesson Corporation, AmerisourceBergen Corporation and Cardinal Health, Inc. [Member]
Derivative [Line Items]
Percentage of accounts receivable represented by customers with largest balances (as percent)	40.00%
Afferent Pharmaceuticals
Derivative [Line Items]
Payments of contingent consideration	$ 175,000,000
Significant Other Observable Inputs (Level 2)
Derivative [Line Items]
Cash and cash equivalents	8,000,000,000
Cash equivalents	$ 7,200,000,000
1.30% notes due 2018 \| Interest Rate Swap
Derivative [Line Items]
Number of interest rate swaps held \| interest_rate_swap			4
Notional amount of derivative			$ 1,000,000,000
Face amount of debt			$ 1,000,000,000.0
Fixed-rate notes, stated interest rate (as percent)			1.30%
5.00% notes due 2019 \| Interest Rate Swap
Derivative [Line Items]
Number of interest rate swaps held \| interest_rate_swap	3
Notional amount of derivative	$ 550,000,000
Face amount of debt	$ 1,250,000,000.00
Fixed-rate notes, stated interest rate (as percent)	5.00%
Derivatives Designated as Hedging Instruments
Derivative [Line Items]
Notional amount of derivative	$ 14,390,000,000	14,386,000,000
Derivatives Not Designated as Hedging Instruments
Derivative [Line Items]
Notional amount of derivative	$ 15,352,000,000	$ 11,209,000,000
Maximum \| Derivatives Designated as Hedging Instruments
Derivative [Line Items]
Maximum planning cycle of third-party sales hedges (no more than)	2 years
Maximum \| Derivatives Not Designated as Hedging Instruments
Derivative [Line Items]
Maximum planning cycle of third-party sales hedges (no more than)	1 year