Segment Information - Reconciliation of Financial Measures of Segments to Consolidated Totals (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenues	$ 61,397	$ 45,693
Net investment income	249	50
Total revenues	61,646	45,743
Adjusted Operating Income (Loss)	3,595	2,293
Pharmacy Services Segment [Member]
Revenues	33,558	32,546
Net investment income	0	0
Total revenues	33,558	32,546
Retail Long-Term Care Segment [Member]
Net investment income	0	0
Total revenues	21,115	20,432
Health Care Benefits Segment [Member]
Total revenues	17,870	1,318
Corporate / Other [Member]
Total revenues	110	48
Operating Segments [Member] | Pharmacy Services Segment [Member]
Net Revenues, Retail CoPayments	3,300	3,300
Revenues	33,558	32,546
Total revenues	33,558	32,546
Adjusted Operating Income (Loss)	947	987
Operating Segments [Member] | Retail Long-Term Care Segment [Member]
Revenues	21,115	20,432
Total revenues	21,115	20,432
Adjusted Operating Income (Loss)	1,489	1,836
Operating Segments [Member] | Health Care Benefits Segment [Member]
Revenues	17,706	1,316
Net investment income	164	2
Total revenues	17,870	1,318
Adjusted Operating Income (Loss)	1,562	(137)
Operating Segments [Member] | Corporate / Other [Member]
Revenues	25	0
Net investment income	85	48
Total revenues	110	48
Adjusted Operating Income (Loss)	(231)	(218)
Intersegment Eliminations [Member]
Revenues	(11,007)	(8,601)
Net investment income	0	0
Total revenues	(11,007)	(8,601)
Adjusted Operating Income (Loss)	$ (172)	$ (175)