Condensed Consolidating Financial Information - Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Premiums									$ 36,113	$ 32,491	$ 30,824
Net investment income									1,480	1,226	1,147
Total revenues	$ 14,300	$ 11,457	$ 11,480	$ 11,413	$ 10,632	$ 10,372	$ 10,374	$ 10,428	48,650	41,806	39,838
Benefits and Expenses
Medical costs and other benefit expenses									27,528	25,263	24,341
Pharmacy and other service costs									4,793	2,456	2,468
Selling, general and administrative expenses									11,934	10,030	9,790
Amortization of other acquired intangible assets									235	115	151
Total benefits and expenses									44,490	37,864	36,750
Income from operations									4,160	3,942	3,088
Interest and other income (expense)									(498)	(252)	(278)
Debt extinguishment costs						(321)			0	(321)	0
Net realized investment gains (losses)									(81)	237	169
Income (loss) before income taxes	228	1,033	1,102	1,218	758	824	1,134	890	3,581	3,606	2,979
Total income taxes									935	1,374	1,136
Net Income									2,646	2,232	1,843
Less: net income (loss) attributable to noncontrolling interests									9	(5)	(24)
Shareholders' net income	$ 144	$ 772	$ 806	$ 915	$ 266	$ 560	$ 813	$ 598	2,637	2,237	1,867
Other comprehensive income (loss), net of tax									(390)	300	(132)
Shareholders' comprehensive income (loss)									2,247	2,537	1,735
Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									5,578	5,110	4,901
Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									5,479	2,979	2,966
Consolidation, Eliminations [Member]
Revenues
Premiums									0	0	0
Net investment income									0	0	0
Total revenues									(1,018)	0	0
Benefits and Expenses
Medical costs and other benefit expenses									0	0	0
Pharmacy and other service costs									(970)	0
Selling, general and administrative expenses									(48)	0	0
Amortization of other acquired intangible assets									0	0	0
Total benefits and expenses									(1,018)	0	0
Income from operations									0	0	0
Interest and other income (expense)									0	0	0
Intercompany interest income (expense)									0	0	0
Debt extinguishment costs										0	0
Net realized investment gains (losses)									0	0	0
Income (loss) before income taxes									0	0	0
Total income taxes									0	0	0
Income before equity in earnings of subsidiaries									0	0	0
Equity in income from subsidiaries									(6,467)	(2,823)	(2,249)
Net Income									(6,467)	(2,823)	(2,249)
Less: net income (loss) attributable to noncontrolling interests									0	0	0
Shareholders' net income									(6,467)	(2,823)	(2,249)
Other comprehensive income (loss), net of tax									926	(269)	154
Shareholders' comprehensive income (loss)									(5,541)	(3,092)	(2,095)
Consolidation, Eliminations [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									(48)	0	0
Consolidation, Eliminations [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									(970)	0	0
Cigna [Member]
Revenues
Net investment income									(123)
Total revenues									123
Benefits and Expenses
Selling, general and administrative expenses									200
Total benefits and expenses									200
Income from operations									(77)
Interest and other income (expense)									(244)
Intercompany interest income (expense)									(5)
Debt extinguishment costs									0
Net realized investment gains (losses)									1
Income (loss) before income taxes									(327)
Total income taxes									(74)
Income before equity in earnings of subsidiaries									(253)
Equity in income from subsidiaries									2,890
Shareholders' net income									2,637
Other comprehensive income (loss), net of tax									(390)
Shareholders' comprehensive income (loss)									2,247
Cigna [Member] | Reportable Legal Entities [Member]
Revenues
Premiums									0	0	0
Net investment income									123	0	0
Total revenues									123	0	0
Benefits and Expenses
Medical costs and other benefit expenses									0	0	0
Pharmacy and other service costs									0	0	0
Selling, general and administrative expenses									200	0	0
Amortization of other acquired intangible assets									0	0	0
Total benefits and expenses									200	0	0
Income from operations									(77)	0	0
Interest and other income (expense)									(244)	0	0
Intercompany interest income (expense)									(5)	0	0
Debt extinguishment costs										0	0
Net realized investment gains (losses)									(1)	0	0
Income (loss) before income taxes									(327)	0	0
Total income taxes									(74)	0	0
Income before equity in earnings of subsidiaries									(253)	0	0
Equity in income from subsidiaries									2,890	0	0
Net Income									2,637	0	0
Less: net income (loss) attributable to noncontrolling interests									0	0	0
Shareholders' net income									2,637	0	0
Other comprehensive income (loss), net of tax									(390)	0	0
Shareholders' comprehensive income (loss)									2,247	0	0
Cigna [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									0	0	0
Cigna [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									0	0	0
Old Cigna [Member]
Revenues
Net investment income										0	0
Total revenues										0	0
Benefits and Expenses
Selling, general and administrative expenses										195	281
Total benefits and expenses										195	281
Income from operations										(195)	(281)
Interest and other income (expense)										(246)	(244)
Intercompany interest income (expense)										(18)	(3)
Debt extinguishment costs										(321)	0
Net realized investment gains (losses)										0	0
Income (loss) before income taxes										(780)	(528)
Total income taxes										(194)	(146)
Income before equity in earnings of subsidiaries										(586)	(382)
Equity in income from subsidiaries										2,823	2,249
Shareholders' net income										2,237	1,867
Other comprehensive income (loss), net of tax										300	(132)
Shareholders' comprehensive income (loss)										2,537	1,735
Old Cigna [Member] | Reportable Legal Entities [Member]
Revenues
Premiums									0	0	0
Net investment income									1	0	0
Total revenues									1	0	0
Benefits and Expenses
Medical costs and other benefit expenses									0	0	0
Pharmacy and other service costs									0	0	0
Selling, general and administrative expenses									535	195	281
Amortization of other acquired intangible assets									0	0	0
Total benefits and expenses									535	195	281
Income from operations									(534)	(195)	(281)
Interest and other income (expense)									(264)	(246)	(244)
Intercompany interest income (expense)									(58)	(18)	(3)
Debt extinguishment costs										(321)	0
Net realized investment gains (losses)									0	0	0
Income (loss) before income taxes									(856)	(780)	(528)
Total income taxes									(163)	(194)	(146)
Income before equity in earnings of subsidiaries									(693)	(586)	(382)
Equity in income from subsidiaries									3,613	2,823	2,249
Net Income									2,920	2,237	1,867
Less: net income (loss) attributable to noncontrolling interests									0	0	0
Shareholders' net income									2,920	2,237	1,867
Other comprehensive income (loss), net of tax									(390)	300	(132)
Shareholders' comprehensive income (loss)									2,530	2,537	1,735
Old Cigna [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									0	0	0
Old Cigna [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									0	0	0
Express Scripts Holding Company [Member] | Reportable Legal Entities [Member]
Revenues
Premiums									0	0	0
Net investment income									2	0	0
Total revenues									2	0	0
Benefits and Expenses
Medical costs and other benefit expenses									0	0	0
Pharmacy and other service costs									0	0	0
Selling, general and administrative expenses									0	0	0
Amortization of other acquired intangible assets									0	0	0
Total benefits and expenses									0	0	0
Income from operations									2	0	0
Interest and other income (expense)									15	0	0
Intercompany interest income (expense)									(15)	0	0
Debt extinguishment costs										0	0
Net realized investment gains (losses)									0	0	0
Income (loss) before income taxes									2	0	0
Total income taxes									0	0	0
Income before equity in earnings of subsidiaries									2	0	0
Equity in income from subsidiaries									(32)	0	0
Net Income									(30)	0	0
Less: net income (loss) attributable to noncontrolling interests									0	0	0
Shareholders' net income									(30)	0	0
Other comprehensive income (loss), net of tax									0	0	0
Shareholders' comprehensive income (loss)									(30)	0	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
Express Scripts Holding Company [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									0	0	0
Express Scripts Incorporated [Member] | Reportable Legal Entities [Member]
Revenues
Premiums									0	0	0
Net investment income									0	0	0
Total revenues									1,889	0	0
Benefits and Expenses
Medical costs and other benefit expenses									0	0	0
Pharmacy and other service costs									1,763	0	0
Selling, general and administrative expenses									44	0	0
Amortization of other acquired intangible assets									94	0	0
Total benefits and expenses									1,901	0	0
Income from operations									(12)	0	0
Interest and other income (expense)									(17)	0	0
Intercompany interest income (expense)									7	0	0
Debt extinguishment costs										0	0
Net realized investment gains (losses)									0	0	0
Income (loss) before income taxes									(22)	0	0
Total income taxes									(4)	0	0
Income before equity in earnings of subsidiaries									(18)	0	0
Equity in income from subsidiaries									(33)	0	0
Net Income									(51)	0	0
Less: net income (loss) attributable to noncontrolling interests									0	0	0
Shareholders' net income									(51)	0	0
Other comprehensive income (loss), net of tax									0	0	0
Shareholders' comprehensive income (loss)									(51)	0	0
Express Scripts Incorporated [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									23	0	0
Express Scripts Incorporated [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									1,866	0	0
Medco Health Solutions Incorporated [Member] | Reportable Legal Entities [Member]
Revenues
Premiums									0	0	0
Net investment income									0	0	0
Total revenues									425	0	0
Benefits and Expenses
Medical costs and other benefit expenses									0	0	0
Pharmacy and other service costs									417	0	0
Selling, general and administrative expenses									8	0	0
Amortization of other acquired intangible assets									13	0	0
Total benefits and expenses									438	0	0
Income from operations									(13)	0	0
Interest and other income (expense)									(10)	0	0
Intercompany interest income (expense)									5	0	0
Debt extinguishment costs										0	0
Net realized investment gains (losses)									0	0	0
Income (loss) before income taxes									(18)	0	0
Total income taxes									(4)	0	0
Income before equity in earnings of subsidiaries									(14)	0	0
Equity in income from subsidiaries									29	0	0
Net Income									15	0	0
Less: net income (loss) attributable to noncontrolling interests									0	0	0
Shareholders' net income									15	0	0
Other comprehensive income (loss), net of tax									0	0	0
Shareholders' comprehensive income (loss)									15	0	0
Medco Health Solutions Incorporated [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									7	0	0
Medco Health Solutions Incorporated [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									418	0	0
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Revenues
Premiums									36,113	32,491	30,824
Net investment income									1,354	1,226	1,147
Total revenues									47,228	41,806	39,838
Benefits and Expenses
Medical costs and other benefit expenses									27,528	25,263	24,341
Pharmacy and other service costs									3,583	2,456	2,468
Selling, general and administrative expenses									11,195	9,835	9,509
Amortization of other acquired intangible assets									128	115	151
Total benefits and expenses									42,434	37,669	36,469
Income from operations									4,794	4,137	3,369
Interest and other income (expense)									22	(6)	(34)
Intercompany interest income (expense)									66	18	3
Debt extinguishment costs										0	0
Net realized investment gains (losses)									(80)	237	169
Income (loss) before income taxes									4,802	4,386	3,507
Total income taxes									1,180	1,568	1,282
Income before equity in earnings of subsidiaries									3,622	2,818	2,225
Equity in income from subsidiaries									0	0	0
Net Income									3,622	2,818	2,225
Less: net income (loss) attributable to noncontrolling interests									9	(5)	(24)
Shareholders' net income									3,613	2,823	2,249
Other comprehensive income (loss), net of tax									(536)	269	(154)
Shareholders' comprehensive income (loss)									3,077	3,092	2,095
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Fees and other revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									5,596	5,110	4,901
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member] | Pharmacy revenues [Member]
Revenues
Pharmacy revenues, fees and other revenues									$ 4,165	$ 2,979	$ 2,966