Medical Costs Payable Rollforward (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 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	522	261
Reported medical costs:
Current year	78,523	72,570
Prior years	(400)	(280)
Total reported medical costs	78,123	72,290
Medical payments:
Payments for current year	(60,707)	(55,738)
Payments for prior years	(16,922)	(15,345)
Total medical payments	(77,629)	(71,083)
Medical costs payable, end of period	$ 20,907	$ 19,339