Acquisition of Aetna (Details) $ / shares in Units, $ in Billions	Nov. 28, 2018 USD ($) $ / shares	Jun. 30, 2019 building clinic
Business Acquisition [Line Items]
Number of stores | building		9,900
Number of walk in medical clinics | clinic		1,100
Aetna Inc.
Business Acquisition [Line Items]
Percentage of voting interests acquired	100.00%
Cash received by shareholders (in dollars per share) | $ / shares	$ 145.00
Per share exchange ratio (in shares) | $ / shares	0.8378
Acquisition value per share acquired (in dollars per share) | $ / shares	$ 212
Consideration transferred | $	$ 70
Acquisition assigned value of acquiree | $	78
Business combination, long-term debt | $	$ 45