Acquisitions, Goodwill, and Acquired Intangible Assets - Additional Information (Details) - USD ($) $ in Millions			3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 11, 2018	Apr. 12, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired			$ 976	$ 13,213	$ 1,855	$ 13,891	$ 1,936	$ 13,893
Ring, Inc [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired		$ 839
PillPack, Inc. [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	$ 753
Other 2018 Acquisitions [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred					$ 46