Segment Reporting (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)
Segment reporting information
Number of reportable segments | segment	3
Net revenues	$ 45,693	$ 44,514
Cost of Goods and Services Sold	38,834	37,943
Gross profit	6,859	6,571
Operating expenses	4,913	4,778
Operating profit (loss)	1,946	1,793
Pharmacy Services Segment
Segment reporting information
Net revenues, retail co-payments	3,300	3,100
Retail/LTC Segment
Segment reporting information
Integration related costs		15
Goodwill, impairment loss	199
Loss on disposal	86
Acquisition related costs	3
Corporate Segment | Operating profit
Segment reporting information
Acquisition related costs	40
Operating Segments | Pharmacy Services Segment
Segment reporting information
Net revenues	32,218	31,223
Cost of Goods and Services Sold		30,141
Gross profit	1,138	1,082
Operating expenses		325
Operating profit (loss)	761	757
Operating Segments | Retail/LTC Segment
Segment reporting information
Net revenues	20,432	19,341
Cost of Goods and Services Sold		13,660
Gross profit	5,916	5,681
Operating expenses		4,248
Operating profit (loss)	1,624	1,433
Operating Segments | Corporate Segment
Segment reporting information
Operating expenses		221
Operating profit (loss)	(264)	(221)
Intersegment Eliminations
Segment reporting information
Net revenues	(6,957)	(6,050)
Cost of Goods and Services Sold		(5,858)
Gross profit	(195)	(192)
Operating expenses		(16)
Operating profit (loss)	$ (175)	(176)
Previously Reported
Segment reporting information
Cost of Goods and Services Sold		37,934
Gross profit		6,580
Operating expenses		4,787
Operating profit (loss)		1,793
Previously Reported | Operating Segments | Pharmacy Services Segment
Segment reporting information
Cost of Goods and Services Sold		30,127
Gross profit		1,096
Operating expenses		312
Operating profit (loss)		784
Previously Reported | Operating Segments | Retail/LTC Segment
Segment reporting information
Cost of Goods and Services Sold		13,665
Gross profit		5,676
Operating expenses		4,265
Operating profit (loss)		1,411
Previously Reported | Operating Segments | Corporate Segment
Segment reporting information
Operating expenses		226
Operating profit (loss)		(226)
Previously Reported | Intersegment Eliminations
Segment reporting information
Cost of Goods and Services Sold		(5,858)
Gross profit		(192)
Operating expenses		(16)
Operating profit (loss)		(176)
Adjustments.
Segment reporting information
Cost of Goods and Services Sold		9
Gross profit		(9)
Operating expenses		(9)
Adjustments. | Operating Segments | Pharmacy Services Segment
Segment reporting information
Cost of Goods and Services Sold		14
Gross profit		(14)
Operating expenses		13
Operating profit (loss)		(27)
Adjustments. | Operating Segments | Retail/LTC Segment
Segment reporting information
Cost of Goods and Services Sold		(5)
Gross profit		5
Operating expenses		(17)
Operating profit (loss)		22
Adjustments. | Operating Segments | Corporate Segment
Segment reporting information
Operating expenses		(5)
Operating profit (loss)		$ 5