Significant Accounting Policies - Amounts Due To Government Agencies (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Medicaid:
Minimum MLR and profit sharing	$ 852	$ 513
Other	249	76
Medicare:
Risk adjustment and Part D risk sharing	87	45
Minimum MLR and profit sharing	82	62
Other	41	30
Marketplace:
Risk adjustment	691	326
Minimum MLR	30	37
Other	49	21
Magellan Complete Care acquisition opening balance	0	143
Medical Premium Liability Due To Agency	$ 2,081	$ 1,253