Medical Claims and Benefits Payable - Medical Claims and Future Benefits (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Fee-for-service claims incurred but not paid (“IBNP”)	$ 1,406	$ 1,562	$ 1,717
Pharmacy payable	126	115	112
Capitation payable	55	52	67
Other	267	232	296
Total	$ 1,854	$ 1,961	$ 2,192	$ 1,929