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Goodwill And Other Intangible Assets (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]    
Estimated amortization expense 2015 $ 184.2us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths  
Estimated amortization expense 2016 153.5us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo  
Estimated amortization expense 2017 133.5us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree  
Estimated amortization expense 2018 113.8us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour  
Estimated amortization expense 2019 94.1us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive  
Goodwill [Line Items]    
Measurement period adjustments 1.8us-gaap_GoodwillPurchaseAccountingAdjustments (27.4)us-gaap_GoodwillPurchaseAccountingAdjustments
Tax benefit on the exercise of stock options [Member]    
Goodwill [Line Items]    
Measurement period adjustments (1.8)us-gaap_GoodwillPurchaseAccountingAdjustments
/ antm_PurchaseAccountingAdjustmentsAxis
= antm_TaxbenefitontheexerciseofstockoptionsMember
(1.5)us-gaap_GoodwillPurchaseAccountingAdjustments
/ antm_PurchaseAccountingAdjustmentsAxis
= antm_TaxbenefitontheexerciseofstockoptionsMember
Other measurement period adjustments [Member]    
Goodwill [Line Items]    
Increase (decrease) related to other measurement period adjustments   $ 28.9antm_IncreaseDecreaseRelatedToOtherPurchaseAccountingAdjustments
/ antm_PurchaseAccountingAdjustmentsAxis
= antm_OthermeasurementperiodadjustmentsMember