Quarterly report pursuant to Section 13 or 15(d)

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

v3.8.0.1
Medical Claims Liability - (Schedule of Change in Medical Claims Liability) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]    
Balance, January 1 $ 4,286 $ 3,929
Less: Reinsurance recoverable 18 5
Balance, January 1, net 4,268 3,924
Acquisitions 0 0
Incurred related to:    
Current year 10,302 9,557
Prior years (263) (235)
Total incurred 10,039 9,322
Paid related to:    
Current year 6,579 5,973
Prior years 2,970 2,991
Total paid 9,549 8,964
Balance at March 31, net 4,758 4,282
Plus: Reinsurance recoverable 13 8
Balance, March 31 $ 4,771 $ 4,290