Summary of Significant Accounting Policies Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 61,397	$ 45,693
Net investment income	249	50
Total revenues	61,646	45,743
Pharmacy Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	33,558	32,546
Net investment income	0	0
Total revenues	33,558	32,546
Retail Long-Term Care Segment [Member]
Disaggregation of Revenue [Line Items]
Net investment income	0	0
Total revenues	21,115	20,432
Health Care Benefits Segment [Member]
Disaggregation of Revenue [Line Items]
Total revenues	17,870	1,318
Corporate / Other [Member]
Disaggregation of Revenue [Line Items]
Total revenues	110	48
Pharmacy
Disaggregation of Revenue [Line Items]
Revenues	38,524	39,305
Pharmacy | Pharmacy Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	33,413	32,406
Pharmacy | Retail Long-Term Care Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	16,118	15,500
Pharmacy | Health Care Benefits Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0
Pharmacy | Corporate / Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0
Front Store
Disaggregation of Revenue [Line Items]
Revenues	4,799	4,726
Front Store | Pharmacy Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0
Front Store | Retail Long-Term Care Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,799	4,726
Front Store | Health Care Benefits Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0
Front Store | Corporate / Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0
Premiums
Disaggregation of Revenue [Line Items]
Revenues	16,282	1,306
Premiums | Pharmacy Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0
Premiums | Retail Long-Term Care Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0
Premiums | Health Care Benefits Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	16,259	1,306
Premiums | Corporate / Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	23	0
Other
Disaggregation of Revenue [Line Items]
Revenues	1,792	356
Other | Pharmacy Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	145	140
Other | Retail Long-Term Care Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	198	206
Other | Health Care Benefits Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,447	10
Other | Corporate / Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	2	0
Pharmacy network | Pharmacy Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	21,574	21,198
Mail choice | Pharmacy Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	11,839	11,208
Other | Pharmacy Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	145	140
Operating Segments [Member] | Pharmacy Services Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	33,558	32,546
Total revenues	33,558	32,546
Operating Segments [Member] | Retail Long-Term Care Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	21,115	20,432
Total revenues	21,115	20,432
Operating Segments [Member] | Health Care Benefits Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	17,706	1,316
Net investment income	164	2
Total revenues	17,870	1,318
Operating Segments [Member] | Corporate / Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	25	0
Net investment income	85	48
Total revenues	110	48
Intersegment Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenues	(11,007)	(8,601)
Net investment income	0	0
Total revenues	(11,007)	(8,601)
Intersegment Eliminations [Member] | Front Store
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations [Member] | Premiums
Disaggregation of Revenue [Line Items]
Revenues	0	0
Intersegment Eliminations [Member] | Other
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 0