Medical Claims and Benefits Payable - Components of Change in Medical Claims and Benefits Payable (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Insurance Claims
Medical claims and benefits payable, beginning balance	$ 1,854	$ 1,961
Components of medical care costs related to:
Current year	11,478	10,613
Prior years	(66)	(253)
Total medical care costs	11,412	10,360
Change in non-risk and other provider payables	50	131
Payments for medical care costs related to:
Current year	9,500	8,996
Prior years	1,527	1,481
Total paid	11,027	10,477
Medical claims and benefits payable, ending balance	$ 2,289	$ 1,975