Debt (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended											9 Months Ended		9 Months Ended							9 Months Ended								9 Months Ended		9 Months Ended			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Senior Revolving Credit	Sep. 30, 2013 Commercial Paper Program	Sep. 30, 2013 Senior Unsecured Notes 6.000%, face amount of $400.0, due 2014	Sep. 30, 2013 Senior Unsecured Notes 5.875%, face amount of $700.0, due 2017	Sep. 30, 2013 Senior Unsecured Notes 7.000%, face amount of $600.0, due 2019	Sep. 30, 2013 Senior Unsecured Notes 5.950%, face amount of $500.0, due 2034	Sep. 30, 2013 Senior Unsecured Notes 5.850%, face amount of $900.0, due 2036	Sep. 30, 2013 Senior Unsecured Notes 6.375%, face amount of $800.0, due 2037	Sep. 30, 2013 Senior Unsecured Notes 5.800%, face amount of $300.0, due 2040	Sep. 30, 2013 Senior Unsecured Notes 2.300%, face amount of $650.0, due 2018	Jul. 30, 2013 Senior Unsecured Notes 2.300%, face amount of $650.0, due 2018	Sep. 30, 2013 Senior Unsecured Notes 5.100%, face amount of $600.0, due 2044	Jul. 30, 2013 Senior Unsecured Notes 5.100%, face amount of $600.0, due 2044	Sep. 30, 2013 Senior Unsecured Notes 7.500%, face amount of $475.0, due 2019	Aug. 13, 2013 Senior Unsecured Notes, First Tender Offer Tranche	Jul. 30, 2013 Senior Unsecured Notes, First Tender Offer Tranche	Jul. 30, 2013 Senior Unsecured Notes, First Tender Offer Tranche 5.875%, face amount of $700.0, due 2017	Jul. 30, 2013 Senior Unsecured Notes, First Tender Offer Tranche 7.000%, face amount of $600.0, due 2019	Sep. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche	Aug. 13, 2013 Senior Unsecured Notes, Second Tender Offer Tranche	Aug. 12, 2013 Senior Unsecured Notes, Second Tender Offer Tranche	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche 5.950%, face amount of $500.0, due 2034	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche 5.850%, face amount of $900.0, due 2036	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche 6.375%, face amount of $800.0, due 2037	Jul. 30, 2013 Senior Unsecured Notes, Second Tender Offer Tranche 5.800%, face amount of $300.0, due 2040	Sep. 30, 2013 Senior Unsecured Notes 6.000%, face amount of $400.0, due 2014	Sep. 05, 2013 Senior Unsecured Notes 6.000%, face amount of $400.0, due 2014	Sep. 30, 2013 Senior Unsecured Notes Tender Offer	Dec. 31, 2012 Amerigroup Senior Unsecured Notes 7.500%, face amount of $475.0, due 2019	Dec. 24, 2012 Amerigroup Senior Unsecured Notes 7.500%, face amount of $475.0, due 2019	Sep. 30, 2013 Amerigroup Senior Unsecured Notes 7.5000% Notes Due 2019
Debt Instrument [Line Items]
Debt Redemption Date																															Sep. 05, 2013		Aug. 13, 2013			Jan. 25, 2013
Debt instrument, principal amount repurchased																			$ 300,000,000.0					$ 400,000,000.0								$ 400,000,000.0
Notes payable, interest rate							6.00%	5.875%	7.00%	5.95%	5.85%	6.375%	5.80%	2.30%	2.30%	5.10%	5.10%	7.50%			5.875%	7.00%					5.95%	5.85%	6.375%	5.80%		6.00%			7.50%
Repayment of senior debt																															411,000,000		837,700,000			555,600,000
Loss on extinguishment of debt	145,300,000	0	145,300,000	0																											10,000,000		135,300,000
Tender offer initiation date																																	Jul. 30, 2013
Repurchase tender offer, maximum amount																				300,000,000.0						300,000,000
Repurchase tender offer, increase subject to management’s election																				100,000,000						100,000,000
Date Of Increase To Tender Offer																							Aug. 12, 2013
Repurchase tender offer, maximum amount after increase																									400,000,000.0
Debt instrument, issuance date														Jul. 30, 2013		Jul. 30, 2013
Debt instrument, face amount							400,000,000	700,000,000	600,000,000	500,000,000	900,000,000	800,000,000	300,000,000	650,000,000	650,000,000.0	600,000,000	600,000,000.0	475,000,000																	475,000,000.0
Minimum ownership percentage of holders to trigger a put feature in an event of default															25.00%
Fair value of debt																																		556,900,000
Ratio of the weighted-average redemption price to the principal amount																																				117.00%
Line of credit facility, maximum borrowing capacity					2,000,000,000.0
Line of credit maturity date					Sep. 29, 2016
Line of credit facility amount outstanding					0
Commercial paper authorized						2,500,000,000.0
Commercial paper	$ 794,900,000		$ 794,900,000