Segment Information - Summarized Segment Financial Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenues from customers	$ 159,157	$ 152,176	$ 47,170
Net investment income	1,244	1,390	1,480
TOTAL REVENUES	160,401	153,566	48,650
Revenue contribution from transitioning clients		(13,347)	(459)
Net realized investment results from certain equity method investments	(130)	(44)	43
Special item related to contractual adjustment for a former client	(204)
Special items reported in integration and transaction-related costs			(123)
Adjusted revenues	160,067	140,175	48,111
Depreciation and amortization	2,802	3,651	695
Income before income taxes	10,868	6,570	3,581
Pre-tax adjustments to reconcile to adjusted income from operations
Adjustment for transitioning clients		(1,726)	(62)
(Income) attributable to noncontrolling interests	(37)	(20)	(14)
Net realized investment (gains) losses	(279)	(221)	124
Amortization of acquired intangible assets	1,982	2,949	235
Special items
Integration and transaction-related costs	527	552	852
Debt extinguishment costs	199	0	0
Charge for organizational efficiency plan	31	207	0
Charges associated with litigation matters	25	51	25
Risk corridors recovery	(101)	0	0
Contractual adjustment for a former client	(204)	0	0
Gain on sale of business	(4,203)	0	0
Charges (benefits) associated with tax reform			2
Pre-tax adjusted income (loss) from operations	8,808	8,362	4,743
Evernorth
Segment Reporting Information [Line Items]
Revenues from customers	112,647	107,354	5,902
U.S. Medical
Segment Reporting Information [Line Items]
Revenues from customers	36,027	34,861	31,759
International Markets
Segment Reporting Information [Line Items]
Revenues from customers	5,853	5,500	5,174
Group Disability and Other
Segment Reporting Information [Line Items]
Revenues from customers	4,630	4,461	4,335
Operating Segments | Evernorth
Segment Reporting Information [Line Items]
Net investment income	32	60	9
TOTAL REVENUES	116,334	109,794	7,065
Revenue contribution from transitioning clients		(13,347)	(459)
Net realized investment results from certain equity method investments	0	0	0
Special item related to contractual adjustment for a former client	(204)
Special items reported in integration and transaction-related costs			0
Adjusted revenues	116,130	96,447	6,606
Depreciation and amortization	2,248	3,071	120
Income before income taxes	3,684	3,983	329
Pre-tax adjustments to reconcile to adjusted income from operations
Adjustment for transitioning clients		(1,726)	(62)
(Income) attributable to noncontrolling interests	(17)	(4)	0
Net realized investment (gains) losses	(17)	0	0
Amortization of acquired intangible assets	1,917	2,839	113
Special items
Integration and transaction-related costs	0	0	0
Debt extinguishment costs	0
Charge for organizational efficiency plan	0	0
Charges associated with litigation matters	0	0	0
Risk corridors recovery	0
Contractual adjustment for a former client	(204)
Gain on sale of business	0
Charges (benefits) associated with tax reform			0
Pre-tax adjusted income (loss) from operations	5,363	5,092	380
Operating Segments | U.S. Medical
Segment Reporting Information [Line Items]
Net investment income	447	478	459
TOTAL REVENUES	38,451	36,519	32,791
Revenue contribution from transitioning clients		0	0
Net realized investment results from certain equity method investments	0	0	0
Special item related to contractual adjustment for a former client	0
Special items reported in integration and transaction-related costs			0
Adjusted revenues	38,451	36,519	32,791
Depreciation and amortization	426	449	466
Income before income taxes	3,956	3,904	3,342
Pre-tax adjustments to reconcile to adjusted income from operations
Adjustment for transitioning clients		0	0
(Income) attributable to noncontrolling interests	0	0	0
Net realized investment (gains) losses	(77)	(112)	36
Amortization of acquired intangible assets	29	69	99
Special items
Integration and transaction-related costs	0	0	0
Debt extinguishment costs	0
Charge for organizational efficiency plan	0	0
Charges associated with litigation matters	0	(30)	25
Risk corridors recovery	(101)
Contractual adjustment for a former client	0
Gain on sale of business	0
Charges (benefits) associated with tax reform			0
Pre-tax adjusted income (loss) from operations	3,807	3,831	3,502
Operating Segments | International Markets
Segment Reporting Information [Line Items]
Net investment income	154	159	149
TOTAL REVENUES	6,007	5,659	5,323
Revenue contribution from transitioning clients		0	0
Net realized investment results from certain equity method investments	(130)	(44)	43
Special item related to contractual adjustment for a former client	0
Special items reported in integration and transaction-related costs			0
Adjusted revenues	5,877	5,615	5,366
Depreciation and amortization	68	87	55
Income before income taxes	1,048	785	670
Pre-tax adjustments to reconcile to adjusted income from operations
Adjustment for transitioning clients		0	0
(Income) attributable to noncontrolling interests	(20)	(16)	(14)
Net realized investment (gains) losses	(161)	(43)	61
Amortization of acquired intangible assets	33	36	18
Special items
Integration and transaction-related costs	0	0	0
Debt extinguishment costs	0
Charge for organizational efficiency plan	0	0
Charges associated with litigation matters	0	0	0
Risk corridors recovery	0
Contractual adjustment for a former client	0
Gain on sale of business	0
Charges (benefits) associated with tax reform			0
Pre-tax adjusted income (loss) from operations	900	762	735
Operating Segments | Group Disability and Other
Segment Reporting Information [Line Items]
Net investment income	611	695	712
TOTAL REVENUES	5,264	5,182	5,061
Revenue contribution from transitioning clients		0	0
Net realized investment results from certain equity method investments	0	0	0
Special item related to contractual adjustment for a former client	0
Special items reported in integration and transaction-related costs			0
Adjusted revenues	5,264	5,182	5,061
Depreciation and amortization	35	41	53
Income before income taxes	4,514	562	497
Pre-tax adjustments to reconcile to adjusted income from operations
Adjustment for transitioning clients		0	0
(Income) attributable to noncontrolling interests	0	0	0
Net realized investment (gains) losses	(24)	(66)	25
Amortization of acquired intangible assets	3	5	5
Special items
Integration and transaction-related costs	0	0	0
Debt extinguishment costs	0
Charge for organizational efficiency plan	0	0
Charges associated with litigation matters	0	0	0
Risk corridors recovery	0
Contractual adjustment for a former client	0
Gain on sale of business	(4,203)
Charges (benefits) associated with tax reform			2
Pre-tax adjusted income (loss) from operations	290	501	529
Corporate and Eliminations
Segment Reporting Information [Line Items]
Net investment income	0	(2)	151
TOTAL REVENUES	(5,655)	(3,588)	(1,590)
Revenue contribution from transitioning clients		0	0
Net realized investment results from certain equity method investments	0	0	0
Special item related to contractual adjustment for a former client	0
Special items reported in integration and transaction-related costs			(123)
Adjusted revenues	(5,655)	(3,588)	(1,713)
Depreciation and amortization	25	3	1
Income before income taxes	(2,334)	(2,664)	(1,257)
Special items
Pre-tax adjusted income (loss) from operations	(1,552)	(1,824)	(403)
Corporate
Segment Reporting Information [Line Items]
Revenues from customers	0	0	0
Pre-tax adjustments to reconcile to adjusted income from operations
Adjustment for transitioning clients		0	0
(Income) attributable to noncontrolling interests	0	0	0
Net realized investment (gains) losses	0	0	2
Amortization of acquired intangible assets	0	0	0
Special items
Integration and transaction-related costs	527	552	852
Debt extinguishment costs	199
Charge for organizational efficiency plan	31	207
Charges associated with litigation matters	25	81	0
Risk corridors recovery	0
Contractual adjustment for a former client	0
Gain on sale of business	0
Charges (benefits) associated with tax reform			0
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues from customers	(5,655)	(3,586)	(1,741)
Intersegment Eliminations | Evernorth
Segment Reporting Information [Line Items]
Revenues from customers	(3,655)	(2,380)	(1,154)
Intersegment Eliminations | U.S. Medical
Segment Reporting Information [Line Items]
Revenues from customers	(1,977)	(1,180)	(573)
Intersegment Eliminations | International Markets
Segment Reporting Information [Line Items]
Revenues from customers	0	0	0
Intersegment Eliminations | Group Disability and Other
Segment Reporting Information [Line Items]
Revenues from customers	$ (23)	$ (26)	$ (14)