Segment Information - Revenue from External Customers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from External Customer [Line Items]
Premiums	$ 42,627	$ 39,714	$ 36,113
Total revenues from external customers	159,157	152,176	47,170
U.S. Medical
Revenue from External Customer [Line Items]
Total revenues from external customers	36,027	34,861	31,759
International Markets
Revenue from External Customer [Line Items]
Premiums	5,511	5,266	5,043
Total revenues from external customers	5,853	5,500	5,174
Pharmacy revenues
Revenue from External Customer [Line Items]
Revenues	107,769	103,099	5,479
Network revenues
Revenue from External Customer [Line Items]
Revenues	53,574	50,431	1,415
Home delivery and specialty revenues
Revenue from External Customer [Line Items]
Revenues	48,792	47,768	3,997
Other
Revenue from External Customer [Line Items]
Revenues	5,403	4,900	67
U.S. Medical premiums | U.S. Medical
Revenue from External Customer [Line Items]
Premiums	32,597	30,089	26,848
Health Insurance | U.S. Medical
Revenue from External Customer [Line Items]
Premiums	13,389	12,523	10,710
Stop loss | U.S. Medical
Revenue from External Customer [Line Items]
Premiums	4,614	4,328	4,008
Other | U.S. Medical
Revenue from External Customer [Line Items]
Premiums	1,135	1,040	1,038
Medicare Advantage | U.S. Medical
Revenue from External Customer [Line Items]
Premiums	7,565	6,314	5,832
Medicare Part D | U.S. Medical
Revenue from External Customer [Line Items]
Premiums	1,593	1,699	764
Other | U.S. Medical
Revenue from External Customer [Line Items]
Premiums	4,301	4,185	4,496
Domestic disability, life and accident premiums
Revenue from External Customer [Line Items]
Premiums	4,423	4,225	4,000
Other premiums
Revenue from External Customer [Line Items]
Premiums	96	134	222
Total services
Revenue from External Customer [Line Items]
Revenues	8,761	9,363	5,578
Fees
Revenue from External Customer [Line Items]
Revenues	8,532	9,229	5,558
Other external revenues
Revenue from External Customer [Line Items]
Revenues	$ 229	$ 134	$ 20