Condensed Consolidating Financial Information - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 20, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Cash and cash equivalents	$ 3,855		$ 2,972	$ 3,185	$ 1,968
Investments	2,045		2,136
Accounts receivable, net	10,473		3,155
Inventories	2,821		228
Other current assets	1,236		820
Total current assets	20,430		9,311
Long-term investments	26,929		26,483
Reinsurance recoverables	5,507		5,763
Deferred policy acquisition costs	2,821		2,237
Property and equipment	4,562		1,563
Investments in subsidiaries	0		0
Intercompany receivables	0		0
Deferred tax assets, net	0		39
Goodwill	44,505		6,164	5,980
Other intangible assets	39,003		345
Other assets	1,630		1,431
Separate account assets	7,839		8,423
TOTAL ASSETS	153,226		61,759
Liabilities Abstract
Current insurance and contractholder liabilities	6,801		6,317
Pharmacy and service costs payable	10,702		305
Accounts payable	4,366		184
Accrued expenses and other liabilities	7,071		3,963
Accounts payable, accrued expenses and other liabilities			4,147
Short-term debt	2,955		240
Total current liabilities	31,895		11,009
Non-current insurance and contractholder liabilities	19,974		20,530
Deferred tax liabilities, net	9,453		0
Other non-current liabilities	3,470		2,838
Intercompany payables	0		0
Long-term debt	39,523		5,199
Separate account liabilities	7,839		8,423
TOTAL LIABILITIES	112,154		47,999
Redeemable noncontrolling interest	37		49
Total shareholders' equity	41,028		13,711
Noncontrolling interests	7		0
Total Equity	41,035		13,711	13,703	12,020
Total liabilities and equity	153,226		61,759
Consolidation, Eliminations [Member]
Assets
Cash and cash equivalents	0		0	0	0
Investments	0		0
Accounts receivable, net	0		0
Inventories	0		0
Other current assets	(210)		0
Total current assets	(210)		0
Long-term investments	0		0
Reinsurance recoverables			0
Deferred policy acquisition costs	0		0
Property and equipment	0		0
Investments in subsidiaries	(173,780)		(22,631)
Intercompany receivables	(39,147)		(3,180)
Deferred tax assets, net			0
Goodwill	0		0
Other intangible assets	0		0
Other assets	(246)		0
Separate account assets	0		0
TOTAL ASSETS	(213,383)		(25,811)
Liabilities Abstract
Current insurance and contractholder liabilities	0		0
Pharmacy and service costs payable	0		0
Accounts payable	0
Accrued expenses and other liabilities	(210)
Accounts payable, accrued expenses and other liabilities			0
Short-term debt	0		0
Total current liabilities	(210)		0
Non-current insurance and contractholder liabilities	0		0
Deferred tax liabilities, net	(246)
Other non-current liabilities	0		0
Intercompany payables	(39,147)		(3,180)
Long-term debt	0		0
Separate account liabilities	0		0
TOTAL LIABILITIES	(39,603)		(3,180)
Redeemable noncontrolling interest	0		0
Total shareholders' equity	(173,780)		(22,631)
Noncontrolling interests	0
Total Equity	(173,780)
Total liabilities and equity	(213,383)		(25,811)
Cigna [Member]
Assets
Cash and cash equivalents	243	$ 0
Other current assets	14
Total current assets	257
Investments in subsidiaries	68,969
Other assets	48
TOTAL ASSETS	69,274
Liabilities Abstract
Short-term debt	0
Total current liabilities	418
Other non-current liabilities	0
Long-term debt	22,863
TOTAL LIABILITIES	28,246
Total shareholders' equity	41,028
Total liabilities and equity	69,274
Cigna [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	243		0	0
Investments	0		0
Accounts receivable, net	0		0
Inventories	0		0
Other current assets	14		0
Total current assets	257		0
Long-term investments	0		0
Reinsurance recoverables	0		0
Deferred policy acquisition costs	0		0
Property and equipment	0		0
Investments in subsidiaries	68,969		0
Intercompany receivables	0		0
Deferred tax assets, net			0
Goodwill	0		0
Other intangible assets	0		0
Other assets	48		0
Separate account assets	0		0
TOTAL ASSETS	69,274		0
Liabilities Abstract
Current insurance and contractholder liabilities	0		0
Pharmacy and service costs payable	0		0
Accounts payable	22
Accrued expenses and other liabilities	396
Accounts payable, accrued expenses and other liabilities			0
Short-term debt	0		0
Total current liabilities	418		0
Non-current insurance and contractholder liabilities	0		0
Deferred tax liabilities, net	0
Other non-current liabilities	0		0
Intercompany payables	4,965		0
Long-term debt	22,863		0
Separate account liabilities	0		0
TOTAL LIABILITIES	28,246		0
Redeemable noncontrolling interest	0		0
Total shareholders' equity	41,028		0
Noncontrolling interests	0
Total Equity	41,028
Total liabilities and equity	69,274		0
Old Cigna [Member]
Assets
Cash and cash equivalents			9	18	16
Other current assets			31
Total current assets			103
Investments in subsidiaries			22,631
Other assets			221
TOTAL ASSETS			23,155
Liabilities Abstract
Short-term debt			231
Total current liabilities			501
Other non-current liabilities			851
Long-term debt			5,112
TOTAL LIABILITIES			9,444
Total shareholders' equity			13,711
Total liabilities and equity			23,155
Old Cigna [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0		9	18	16
Investments	0		63
Accounts receivable, net	0		0
Inventories	0		0
Other current assets	59		31
Total current assets	59		103
Long-term investments	10		0
Reinsurance recoverables	0		0
Deferred policy acquisition costs	0		0
Property and equipment	0		0
Investments in subsidiaries	27,544		22,631
Intercompany receivables	4,505		200
Deferred tax assets, net			221
Goodwill	0		0
Other intangible assets	0		0
Other assets	198		0
Separate account assets	0		0
TOTAL ASSETS	32,316		23,155
Liabilities Abstract
Current insurance and contractholder liabilities	0		0
Pharmacy and service costs payable	0		0
Accounts payable	0
Accrued expenses and other liabilities	182
Accounts payable, accrued expenses and other liabilities			270
Short-term debt	1,500		231
Total current liabilities	1,682		501
Non-current insurance and contractholder liabilities	0		0
Deferred tax liabilities, net	0
Other non-current liabilities	685		851
Intercompany payables	4,361		2,980
Long-term debt	5,110		5,112
Separate account liabilities	0		0
TOTAL LIABILITIES	11,838		9,444
Redeemable noncontrolling interest	0		0
Total shareholders' equity	20,478		13,711
Noncontrolling interests	0
Total Equity	20,478
Total liabilities and equity	32,316		23,155
Express Scripts Holding Company [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	633		0	0	0
Investments	0		0
Accounts receivable, net	0		0
Inventories	0		0
Other current assets	0		0
Total current assets	633		0
Long-term investments	0		0
Reinsurance recoverables	0		0
Deferred policy acquisition costs	0		0
Property and equipment	0		0
Investments in subsidiaries	52,035		0
Intercompany receivables	0		0
Deferred tax assets, net			0
Goodwill	31,049		0
Other intangible assets	8,400		0
Other assets	0		0
Separate account assets	0		0
TOTAL ASSETS	92,117		0
Liabilities Abstract
Current insurance and contractholder liabilities	0		0
Pharmacy and service costs payable	0		0
Accounts payable	0
Accrued expenses and other liabilities	129
Accounts payable, accrued expenses and other liabilities			0
Short-term debt	995		0
Total current liabilities	1,124		0
Non-current insurance and contractholder liabilities	0		0
Deferred tax liabilities, net	2,001
Other non-current liabilities	0		0
Intercompany payables	29,569		0
Long-term debt	10,932		0
Separate account liabilities	0		0
TOTAL LIABILITIES	43,626		0
Redeemable noncontrolling interest	0		0
Total shareholders' equity	48,491		0
Noncontrolling interests	0
Total Equity	48,491
Total liabilities and equity	92,117		0
Express Scripts Incorporated [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	43		0	0	0
Investments	0		0
Accounts receivable, net	4,206		0
Inventories	0		0
Other current assets	310		0
Total current assets	4,559		0
Long-term investments	0		0
Reinsurance recoverables	0		0
Deferred policy acquisition costs	0		0
Property and equipment	2,432		0
Investments in subsidiaries	17,115		0
Intercompany receivables	7,425		0
Deferred tax assets, net			0
Goodwill	0		0
Other intangible assets	18,962		0
Other assets	68		0
Separate account assets	0		0
TOTAL ASSETS	50,561		0
Liabilities Abstract
Current insurance and contractholder liabilities	0		0
Pharmacy and service costs payable	8,422		0
Accounts payable	834
Accrued expenses and other liabilities	1,387
Accounts payable, accrued expenses and other liabilities			0
Short-term debt	353		0
Total current liabilities	10,996		0
Non-current insurance and contractholder liabilities	0		0
Deferred tax liabilities, net	5,012
Other non-current liabilities	497		0
Intercompany payables	0		0
Long-term debt	24		0
Separate account liabilities	0		0
TOTAL LIABILITIES	16,529		0
Redeemable noncontrolling interest	0		0
Total shareholders' equity	34,032		0
Noncontrolling interests	0
Total Equity	34,032
Total liabilities and equity	50,561		0
Medco Health Solutions Incorporated [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	0		0	0	0
Investments	0		0
Accounts receivable, net	748		0
Inventories	0		0
Other current assets	0		0
Total current assets	748		0
Long-term investments	0		0
Reinsurance recoverables	0		0
Deferred policy acquisition costs	0		0
Property and equipment	0		0
Investments in subsidiaries	8,117		0
Intercompany receivables	2,335		0
Deferred tax assets, net			0
Goodwill	0		0
Other intangible assets	7,040		0
Other assets	74		0
Separate account assets	0		0
TOTAL ASSETS	18,314		0
Liabilities Abstract
Current insurance and contractholder liabilities	0		0
Pharmacy and service costs payable	1,579		0
Accounts payable	4
Accrued expenses and other liabilities	189
Accounts payable, accrued expenses and other liabilities			0
Short-term debt	0		0
Total current liabilities	1,772		0
Non-current insurance and contractholder liabilities	0		0
Deferred tax liabilities, net	1,685
Other non-current liabilities	290		0
Intercompany payables	0		0
Long-term debt	506		0
Separate account liabilities	0		0
TOTAL LIABILITIES	4,253		0
Redeemable noncontrolling interest	0		0
Total shareholders' equity	14,061		0
Noncontrolling interests	0
Total Equity	14,061
Total liabilities and equity	18,314		0
Non-Guarantor Subsidiaries [Member] | Reportable Legal Entities [Member]
Assets
Cash and cash equivalents	2,936		2,963	$ 3,167	$ 1,952
Investments	2,045		2,073
Accounts receivable, net	5,519		3,155
Inventories	2,821		228
Other current assets	1,063		789
Total current assets	14,384		9,208
Long-term investments	26,919		26,483
Reinsurance recoverables	5,507		5,763
Deferred policy acquisition costs	2,821		2,237
Property and equipment	2,130		1,563
Investments in subsidiaries	0		0
Intercompany receivables	24,882		2,980
Deferred tax assets, net			(182)
Goodwill	13,456		6,164
Other intangible assets	4,601		345
Other assets	1,488		1,431
Separate account assets	7,839		8,423
TOTAL ASSETS	104,027		64,415
Liabilities Abstract
Current insurance and contractholder liabilities	6,801		6,317
Pharmacy and service costs payable	701		305
Accounts payable	3,506
Accrued expenses and other liabilities	4,998
Accounts payable, accrued expenses and other liabilities			3,877
Short-term debt	107		9
Total current liabilities	16,113		10,508
Non-current insurance and contractholder liabilities	19,974		20,530
Deferred tax liabilities, net	1,001
Other non-current liabilities	1,998		1,987
Intercompany payables	252		200
Long-term debt	88		87
Separate account liabilities	7,839		8,423
TOTAL LIABILITIES	47,265		41,735
Redeemable noncontrolling interest	37		49
Total shareholders' equity	56,718		22,631
Noncontrolling interests	7
Total Equity	56,725
Total liabilities and equity	$ 104,027		$ 64,415