Medical Costs Payable Rollforward (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Medical costs payable, beginning of period	$ 19,891	$ 17,871
Acquisitions	868	333
Reported medical costs:
Current year	117,624	108,658
Prior years	(460)	(210)
Total reported medical costs	117,164	108,448
Medical payments:
Payments for current year	(99,487)	(90,348)
Payments for prior years	(17,497)	(16,454)
Total medical payments	(116,984)	(106,802)
Medical costs payable, end of period	$ 20,939	$ 19,850