Quarterly report pursuant to Section 13 or 15(d)

Organization and Operations (Details)

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Organization and Operations (Details) - USD ($)
$ in Millions
Jul. 01, 2018
Sep. 30, 2018
Mar. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Sep. 30, 2017
Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]              
Restricted cash and cash equivalents   $ 7     $ 17 $ 6 $ 6
Cumulative effect adjustment to retained earnings       $ 15      
Retained Earnings              
New Accounting Pronouncements or Change in Accounting Principle [Line Items]              
Cumulative effect adjustment to retained earnings       $ 15      
Retained Earnings | Accounting Standards Codification Topic 606              
New Accounting Pronouncements or Change in Accounting Principle [Line Items]              
Cumulative effect adjustment to retained earnings     $ 16        
Fidelis Care              
New Accounting Pronouncements or Change in Accounting Principle [Line Items]              
Consideration transferred $ 3,470