Quarterly report pursuant to Section 13 or 15(d)

Medical Claims Liability (Schedule of Change in Medical Claims Liability) (Details)

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Medical Claims Liability (Schedule of Change in Medical Claims Liability) (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]    
Balance, January 1 $ 3,929 $ 2,298
Less: Reinsurance Recoverable 5 0
Balance , Net 3,924 2,298
Acquisitions 0 1,462
Incurred related to:    
Current year 19,087 13,940
Prior years (352) (244)
Total incurred 18,735 13,696
Paid related to:    
Current year 15,477 11,626
Prior years 3,022 1,880
Total paid 18,499 13,506
Balance, Net 4,160 3,950
Plus: Reinsurance Recoverable 10 0
Balance, June 30 $ 4,170 $ 3,950