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
9 Months Ended
Sep. 30, 2017
Sep. 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, January 1, net 3,924 2,298
Acquisitions 0 1,453
Incurred related to:    
Current year 28,666 22,372
Prior years (388) (300)
Total incurred 28,278 22,072
Paid related to:    
Current year 24,787 20,121
Prior years 3,099 1,935
Total paid 27,886 22,056
Balance at September 30, net 4,316 3,767
Plus: Reinsurance Recoverable 17 0
Balance, September 30 $ 4,333 $ 3,767