Medical Claims and Benefits Payable - Reconciliation of Claims Development (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Incurred claims and allocated claims adjustment expenses	$ 46,125
Less: cumulative paid claims and allocated claims adjustment expenses	(44,460)
All outstanding liabilities before 2017	15
Non-risk and other provider payables	174
Total	$ 1,854	$ 1,961	$ 2,192	$ 1,929