Condensed Consolidating Financial Information - Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues
Premiums	$ 9,935	$ 8,994	$ 29,709	$ 27,005
Net investment income	349	355	1,035	1,036
Total revenues	38,556	11,457	115,321	34,350
Benefits and Expenses
Medical costs and other benefit expenses	7,734	6,803	22,930	20,420
Pharmacy and other service costs	24,552	602	73,565	1,776
Selling, general and administrative expenses	3,413	2,872	10,096	8,454
Amortization of other acquired intangible assets	734	48	2,214	99
Total benefits and expenses	36,433	10,325	108,805	30,749
Income from operations	2,123	1,132	6,516	3,601
Interest and other income (expense)	(411)	(99)	(1,291)	(212)
Intercompany interest income (expense)	0	0	0	0
Net realized investment gains (losses)	51	0	84	(36)
Income (loss) before income taxes	1,763	1,033	5,309	3,353
Total income taxes	409	259	1,173	854
Income before equity in earnings of subsidiaries	1,354	774	4,136	2,499
Equity in income from subsidiaries	0	0	0	0
Net Income	1,354	774	4,136	2,499
Less: net income (loss) attributable to noncontrolling interests	3	2	9	6
Shareholders' net income	1,351	772	4,127	2,493
Other comprehensive income (loss), net of tax	107	(14)	853	(536)
Shareholders' comprehensive income (loss)	1,458	758	4,980	1,957
Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	2,285	1,361	7,123	4,087
Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	25,987	747	77,454	2,222
Consolidation, Eliminations [Member]
Revenues
Premiums	0	0	0	0
Net investment income	0	0	0	0
Total revenues	(15,727)	0	(40,020)	0
Benefits and Expenses
Medical costs and other benefit expenses	5	0	(31)	0
Pharmacy and other service costs	(14,641)	0	(36,937)	0
Selling, general and administrative expenses	(1,091)	0	(3,052)	0
Amortization of other acquired intangible assets	0	0	0	0
Total benefits and expenses	(15,727)	0	(40,020)	0
Income from operations	0	0	0	0
Interest and other income (expense)	0	0	0	0
Intercompany interest income (expense)	0	0	0	0
Net realized investment gains (losses)	0	0	0	0
Income (loss) before income taxes	0	0	0	0
Total income taxes	0	0	0	0
Income before equity in earnings of subsidiaries	0	0	0	0
Equity in income from subsidiaries	(3,914)	(1,746)	(11,533)	(5,517)
Net Income	(3,914)	(1,746)	(11,533)	(5,517)
Less: net income (loss) attributable to noncontrolling interests	0	0	0	0
Shareholders' net income	(3,914)	(1,746)	(11,533)	(5,517)
Other comprehensive income (loss), net of tax	(186)	39	(1,655)	1,108
Shareholders' comprehensive income (loss)	(4,100)	(1,707)	(13,188)	(4,409)
Consolidation, Eliminations [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	(5,495)	0	(8,683)	0
Consolidation, Eliminations [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	(10,232)	0	(31,337)	0
Cigna [Member] | Reportable Legal Entities [Member]
Revenues
Premiums	0	0	0	0
Net investment income	0	13	(8)	13
Total revenues	0	13	(8)	13
Benefits and Expenses
Medical costs and other benefit expenses	0	0	0	0
Pharmacy and other service costs	0	0	0	0
Selling, general and administrative expenses	0	0	(99)	0
Amortization of other acquired intangible assets	0	0	0	0
Total benefits and expenses	0	0	(99)	0
Income from operations	0	13	91	13
Interest and other income (expense)	(229)	(33)	(695)	(33)
Intercompany interest income (expense)	(28)	0	(93)	0
Net realized investment gains (losses)	0	0	0	0
Income (loss) before income taxes	(257)	(20)	(697)	(20)
Total income taxes	(60)	(4)	(166)	(4)
Income before equity in earnings of subsidiaries	(197)	(16)	(531)	(16)
Equity in income from subsidiaries	1,548	788	4,658	2,509
Net Income	1,351	772	4,127	2,493
Less: net income (loss) attributable to noncontrolling interests	0	0	0	0
Shareholders' net income	1,351	772	4,127	2,493
Other comprehensive income (loss), net of tax	107	(14)	853	(536)
Shareholders' comprehensive income (loss)	1,458	758	4,980	1,957
Cigna [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	0	0	0	0
Cigna [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	0	0	0	0
Old Cigna [Member] | Reportable Legal Entities [Member]
Revenues
Premiums	0	0	0	0
Net investment income	0	1	0	1
Total revenues	0	1	0	1
Benefits and Expenses
Medical costs and other benefit expenses	0	0	0	0
Pharmacy and other service costs	0	0	0	0
Selling, general and administrative expenses	74	126	234	361
Amortization of other acquired intangible assets	0	0	0	0
Total benefits and expenses	74	126	234	361
Income from operations	(74)	(125)	(234)	(360)
Interest and other income (expense)	(57)	(64)	(197)	(191)
Intercompany interest income (expense)	(14)	(16)	(25)	(50)
Net realized investment gains (losses)	0	0	0	0
Income (loss) before income taxes	(145)	(205)	(456)	(601)
Total income taxes	(21)	(35)	(88)	(102)
Income before equity in earnings of subsidiaries	(124)	(170)	(368)	(499)
Equity in income from subsidiaries	1,083	958	3,304	3,008
Net Income	959	788	2,936	2,509
Less: net income (loss) attributable to noncontrolling interests	0	0	0	0
Shareholders' net income	959	788	2,936	2,509
Other comprehensive income (loss), net of tax	108	(14)	851	(536)
Shareholders' comprehensive income (loss)	1,067	774	3,787	1,973
Old Cigna [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	0	0	0	0
Old Cigna [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	0	0	0	0
Express Scripts Holding Company [Member] | Reportable Legal Entities [Member]
Revenues
Premiums	0	0	0	0
Net investment income	(15)	0	27	0
Total revenues	(15)	0	27	0
Benefits and Expenses
Medical costs and other benefit expenses	0	0	0	0
Pharmacy and other service costs	0	0	0	0
Selling, general and administrative expenses	29	0	72	0
Amortization of other acquired intangible assets	0	0	0	0
Total benefits and expenses	29	0	72	0
Income from operations	(44)	0	(45)	0
Interest and other income (expense)	(115)	0	(361)	0
Intercompany interest income (expense)	153	0	399	0
Net realized investment gains (losses)	0	0	0	0
Income (loss) before income taxes	(6)	0	(7)	0
Total income taxes	(1)	0	(1)	0
Income before equity in earnings of subsidiaries	(5)	0	(6)	0
Equity in income from subsidiaries	594	0	1,728	0
Net Income	589	0	1,722	0
Less: net income (loss) attributable to noncontrolling interests	0	0	0	0
Shareholders' net income	589	0	1,722	0
Other comprehensive income (loss), net of tax	(1)	0	2	0
Shareholders' comprehensive income (loss)	588	0	1,724	0
Express Scripts Holding Company [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	0	0	0	0
Express Scripts Holding Company [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	0	0	0	0
Express Scripts Incorporated [Member] | Reportable Legal Entities [Member]
Revenues
Premiums	0	0	0	0
Net investment income	3	0	10	0
Total revenues	18,953	0	55,975	0
Benefits and Expenses
Medical costs and other benefit expenses	1	0	1	0
Pharmacy and other service costs	17,421	0	51,444	0
Selling, general and administrative expenses	991	0	2,750	0
Amortization of other acquired intangible assets	573	0	1,724	0
Total benefits and expenses	18,986	0	55,919	0
Income from operations	(33)	0	56	0
Interest and other income (expense)	0	0	(7)	0
Intercompany interest income (expense)	(58)	0	(181)	0
Net realized investment gains (losses)	0	0	0	0
Income (loss) before income taxes	(91)	0	(132)	0
Total income taxes	(25)	0	(46)	0
Income before equity in earnings of subsidiaries	(66)	0	(86)	0
Equity in income from subsidiaries	574	0	1,549	0
Net Income	508	0	1,463	0
Less: net income (loss) attributable to noncontrolling interests	0	0	0	0
Shareholders' net income	508	0	1,463	0
Other comprehensive income (loss), net of tax	(1)	0	2	0
Shareholders' comprehensive income (loss)	507	0	1,465	0
Express Scripts Incorporated [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	224	0	639	0
Express Scripts Incorporated [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	18,726	0	55,326	0
Medco Health Solutions Incorporated [Member] | Reportable Legal Entities [Member]
Revenues
Premiums	0	0	0	0
Net investment income	3	0	8	0
Total revenues	3,208	0	10,360	0
Benefits and Expenses
Medical costs and other benefit expenses	0	0	0	0
Pharmacy and other service costs	3,004	0	9,670	0
Selling, general and administrative expenses	120	0	438	0
Amortization of other acquired intangible assets	82	0	247	0
Total benefits and expenses	3,206	0	10,355	0
Income from operations	2	0	5	0
Interest and other income (expense)	(5)	0	(19)	0
Intercompany interest income (expense)	(38)	0	(115)	0
Net realized investment gains (losses)	0	0	0	0
Income (loss) before income taxes	(41)	0	(129)	0
Total income taxes	(14)	0	(80)	0
Income before equity in earnings of subsidiaries	(27)	0	(49)	0
Equity in income from subsidiaries	115	0	294	0
Net Income	88	0	245	0
Less: net income (loss) attributable to noncontrolling interests	0	0	0	0
Shareholders' net income	88	0	245	0
Other comprehensive income (loss), net of tax	0	0	0	0
Shareholders' comprehensive income (loss)	88	0	245	0
Medco Health Solutions Incorporated [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	40	0	133	0
Medco Health Solutions Incorporated [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	3,165	0	10,219	0
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Premiums	9,935	8,994	29,709	27,005
Net investment income	358	341	998	1,022
Total revenues	32,137	11,443	88,987	34,336
Benefits and Expenses
Medical costs and other benefit expenses	7,728	6,803	22,960	20,420
Pharmacy and other service costs	18,768	602	49,388	1,776
Selling, general and administrative expenses	3,290	2,746	9,753	8,093
Amortization of other acquired intangible assets	79	48	243	99
Total benefits and expenses	29,865	10,199	82,344	30,388
Income from operations	2,272	1,244	6,643	3,948
Interest and other income (expense)	(5)	(2)	(12)	12
Intercompany interest income (expense)	(15)	16	15	50
Net realized investment gains (losses)	51	0	84	(36)
Income (loss) before income taxes	2,303	1,258	6,730	3,974
Total income taxes	530	298	1,554	960
Income before equity in earnings of subsidiaries	1,773	960	5,176	3,014
Equity in income from subsidiaries	0	0	0	0
Net Income	1,773	960	5,176	3,014
Less: net income (loss) attributable to noncontrolling interests	3	2	9	6
Shareholders' net income	1,770	958	5,167	3,008
Other comprehensive income (loss), net of tax	80	(25)	800	(572)
Shareholders' comprehensive income (loss)	1,850	933	5,967	2,436
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	7,516	1,361	15,034	4,087
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues	$ 14,328	$ 747	$ 43,246	$ 2,222