Medical Claims and Benefits Payable - Components of Change in Medical Claims and Benefits Payable (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Insurance Claims
Medical claims and benefits payable, beginning balance	$ 1,854	$ 1,961
Components of medical care costs related to:
Current period	3,817	3,560
Prior periods	(101)	(189)
Total medical care costs	3,716	3,371
Change in non-risk and other provider payables	(10)	171
Payments for medical care costs related to:
Current period	2,274	2,197
Prior periods	1,305	1,311
Total paid	3,579	3,508
Medical claims and benefits payable, ending balance	$ 1,981	$ 1,995