Segment Reporting - Reconciliation of Operating Earnings to Net Income (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) store	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) store	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 09, 2018 USD ($)
Segment Reporting Information [Line Items]
Operating income (GAAP measure)	$ 3,037,000,000	$ 2,928,000,000	$ 3,332,000,000	$ 2,690,000,000	$ 824,000,000	$ 2,574,000,000	$ (1,373,000,000)	$ 1,996,000,000	$ 11,987,000,000	$ 4,021,000,000	$ 9,538,000,000
Amortization of intangible assets									2,436,000,000	1,006,000,000	817,000,000
Acquisition-related transaction and integration costs									480,000,000	492,000,000	65,000,000
Charges in connection with store rationalization									231,000,000	0	215,000,000
Loss on divestiture of subsidiary									(205,000,000)	(86,000,000)	(9,000,000)
Goodwill impairments		0							0	6,149,000,000	181,000,000
Impairment of long-lived assets									0	43,000,000	0
Interest income on financing for the Aetna Acquisition									0	(536,000,000)	0
Adjusted operating income									$ 15,339,000,000	11,261,000,000	10,825,000,000
Retail/ LTC
Segment Reporting Information [Line Items]
Charges in connection with store rationalization		$ 96,000,000		$ 135,000,000							215,000,000
Goodwill impairments										6,149,000,000	$ 181,000,000
Number of under performing stores | store		22		46
RX Crossroads
Segment Reporting Information [Line Items]
Loss on divestiture of subsidiary										$ 725,000,000
2018 Senior Notes
Segment Reporting Information [Line Items]
Debt issued in acquisition												$ 40,000,000,000