Medical Costs Payable Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Medical costs payable, beginning of period	$ 21,690	$ 19,891
Acquisitions	0	35
Reported medical costs:
Current year	41,580	39,239
Prior years	(580)	(300)
Total reported medical costs	41,000	38,939
Medical payments:
Payments for current year	(23,471)	(22,973)
Payments for prior years	(16,447)	(14,753)
Total medical payments	(39,918)	(37,726)
Medical costs payable, end of period	$ 22,772	$ 21,139