|**Quarterly Financial Data (Unaudited) (Tables)** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
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|**Quarterly Financial Data [Abstract]**           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|Schedule of quarterly financial information       | The following tables present unaudited quarterly financial data.2015(In millions, except per share data)FirstSecondThirdFourthFull YearRevenues$2,352$2,327$2,153$2,269$9,101Net income (loss) (a)$233$138$178$(70)$479Basic earnings (loss) per share$0.86$0.51$0.66$(0.26)$1.77Diluted earnings (loss) per share$0.86$0.51$0.66$(0.26)$1.772014(In millions, except per share data)FirstSecondThirdFourthFull YearRevenues$2,463$2,440$2,411$2,378$9,692Net income (loss) (b)$13$267$213$198$691Basic earnings (loss) per share$0.05$0.99$0.79$0.73$2.56Diluted earnings (loss) per share$0.05$0.98$0.79$0.73$2.55(a)Net income in the fourth quarter of 2015 included a charge related to recognition of a premium deficiency in our long term care business.(b)Net income in the first quarter of 2014 included the impairment loss on the sale of CAC.
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|2015                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|(In millions, except per share data)              | First                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Revenues                                          | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net income (loss) (a)                             | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Basic earnings (loss) per share                   | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Diluted earnings (loss) per share                 | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
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|2014                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
|(In millions, except per share data)              | First                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      
|Revenues                                          | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Net income (loss) (b)                             | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Basic earnings (loss) per share                   | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
|Diluted earnings (loss) per share                 | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
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|(a)                                               | Net income in the fourth quarter of 2015 included a charge related to recognition of a premium deficiency in our long term care business.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
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|(b)                                               | Net income in the first quarter of 2014 included the impairment loss on the sale of CAC.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   

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