Annual report pursuant to Section 13 and 15(d)

Acquisitions - Schedule of Preliminary Allocation of Fair Value of Assets Acquired and Liabilities Assumed (Details)

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Acquisitions - Schedule of Preliminary Allocation of Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($)
$ in Millions
Jul. 01, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Business Acquisition [Line Items]        
Goodwill   $ 6,863 $ 7,015 $ 4,749
Acquired finite-lived intangible assets, weighted average useful life 13 years      
Fidelis Care        
Business Acquisition [Line Items]        
Cash and cash equivalents $ 2,001      
Premium and related receivables 442      
Other current assets 32      
Restricted deposits 495      
Property, software and equipment 48      
Intangible assets 956      
Other long-term assets 2      
Total assets acquired 3,976      
Medical claims liability 1,218      
Accounts payable and accrued expenses 238      
Return of premium payable 123      
Unearned revenue 115      
Other long-term liabilities 324      
Total liabilities assumed 2,018      
Total identifiable net assets 1,958      
Goodwill 1,663      
Total assets acquired and liabilities assumed $ 3,621      
Acquired finite-lived intangible assets, weighted average useful life 13 years      
Fidelis Care | Customer relationships        
Business Acquisition [Line Items]        
Intangible assets $ 711      
Acquired finite-lived intangible assets, weighted average useful life 11 years      
Fidelis Care | Trade names        
Business Acquisition [Line Items]        
Intangible assets $ 196      
Acquired finite-lived intangible assets, weighted average useful life 20 years      
Fidelis Care | Provider contracts        
Business Acquisition [Line Items]        
Intangible assets $ 33      
Acquired finite-lived intangible assets, weighted average useful life 15 years      
Fidelis Care | Developed technologies        
Business Acquisition [Line Items]        
Intangible assets $ 16      
Acquired finite-lived intangible assets, weighted average useful life 2 years