ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012 regions offerings reporting_units		Dec. 31, 2011 offerings		Dec. 31, 2010 offerings
Total Members [Abstract]
Members served by Company products		5,000,000
Significant Customer [Abstract]
Significant customer as percentage of revenues (in hundredths)		10.00%
Number of Part D products		3		2		5
Percentage of Medicaid revenue for KY and State of MO		33.20%		23.80%
Number of Auto Assign Regions		8
Other Receivables [Abstract]
Pharmacy rebate receivables		$ 305,400,000		$ 280,500,000
Business Combinations, Accounting for Goodwill and Other Intangibles [Abstract]
Number of reporting units		6
Change in Medical Claims Liabilities [Roll Forward]
Medical liabilities, beginning of year	1,308,507,000	1,308,507,000		1,237,690,000		1,605,407,000
Acquisitions		50,261,000	[1]	0	[1]	71,548,000	[1]
Reported Medical Costs
Current year		10,984,974,000		9,163,009,000		8,507,460,000
Prior year development		(131,200,000)		(121,607,000)		(241,513,000)
Total reported medical costs		10,853,774,000		9,041,402,000		8,265,947,000
Claim Payments
Payments for current year		9,721,411,000		7,953,744,000		7,491,891,000
Payments for prior year		1,070,398,000		989,783,000		1,185,476,000
Total claim payments		10,791,809,000		8,943,527,000		8,677,367,000
Change in Part D Related Subsidy Liabilities		(1,819,000)		(27,058,000)		(27,845,000)
Medical liabilities, end of year		1,418,914,000		1,308,507,000		1,237,690,000
Supplemental Information
Prior year development (in hundredths)		1.50%	[2]	1.50%	[2]	2.20%	[2]
Current year paid percent (in hundredths)		88.50%	[3]	86.80%	[3]	88.10%	[3]
Comprehensive Income [Abstract]
Deferred tax provision on unrealized holding gains from investments		21,100,000		18,300,000		4,100,000
Deferred tax provision on reclassification adjustments for gains on investments		15,600,000		6,500,000		4,300,000
CMS Receivables and Payables [Abstract]
Total Medicare Part D CMS Receivables, net		381,006,000		299,837,000
Total Medicare Part D CMS Payables, net		(3,091,000)		(3,619,000)
Revenue Recognition [Abstract]
Term of run out provision related to quota share arrangements (in years)						3 years
Ceded premium revenue		45,300,000		43,300,000		49,800,000
RADV Release	133,000,000	132,977,000		0		0
Minimum Loss Ratio Large Employer Group (in hundredths)		85.00%
Minimum Loss Ratio Small Employer Group (in hundredths)		80.00%
Minimum Loss Ratio Individual (in hundredths)		80.00%
Contract Acquisition Costs [Abstract]
Amortization period for acquired contract costs (in years)		1 year
Earnings Per Share [Abstract]
Potential common stock equivalents excluded from computation of computation of diluted earnings per share (in shares)		5,600,000		6,500,000		10,000,000
Management Services Revenue [Member] | Mail Handlers Benefit Plan [Member]
Significant Customer [Abstract]
Significant customer as percentage of revenues (in hundredths)		11.70%		10.00%		11.20%
Managed Care Premiums [Member] | Federal Medicare Program [Member]
Significant Customer [Abstract]
Significant customer as percentage of revenues (in hundredths)		34.20%		32.70%		35.60%
Managed Care Premiums [Member] | State-Sponsored Medicaid Program [Member]
Significant Customer [Abstract]
Significant customer as percentage of revenues (in hundredths)		21.70%		12.50%		10.90%
Jaguar Merger Subsidiary, Inc. [Member]
Business Combinations [Abstract]
Price per share paid in cash		27.30
Amount of Aetna common share recieved per Coventry common share		0.3885
Estimated purchase price		$ 7,300,000,000
Shares of common stock voting at stockholder special meeting		104,941,398
Percent of shares voting in favor of Merger		99.00%
Ratio of shares voting in favor or Merger to total outstanding shares of common stock		78.00%
Minimum [Member]
Property and Equipment [Abstract]
Estimated useful life of long lived, physical assets		3 years
Business Combinations, Accounting for Goodwill and Other Intangibles [Abstract]
Amortization of other acquired intangible assets, minimum (in years)		3 years
Maximum [Member]
Property and Equipment [Abstract]
Estimated useful life of long lived, physical assets		30 years
Business Combinations, Accounting for Goodwill and Other Intangibles [Abstract]
Amortization of other acquired intangible assets, minimum (in years)		20 years

[1] Acquisition balances represent medical liabilities of the acquired company as of the applicable acquisition date.

[2] Prior year reported medical costs in the current year as a percentage of prior year reported medical costs.

[3] Current year claim payments as a percentage of current year reported medical costs.