Insurance and Contractholder Liabilities - U.S. Medical - Summary of Incurred and Paid Claims Development, Claims Frequency Metrics and Incurred but Not Yet Reported Liabilities (Details) - U.S. Medical claim in Millions, $ in Millions	Dec. 31, 2020 USD ($) claim	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Claims Development [Line Items]
Incurred Costs	$ 48,138
Unpaid Claims & Claim Expenses	2,824
Cumulative Costs Paid	45,314
Outstanding liabilities for the periods presented, net of reinsurance	2,824
Other long-duration liabilities not included in development table above	136
Net unpaid claims and claims expenses - U.S. Medical	2,960		$ 2,433	$ 2,158
Reinsurance and other amounts recoverable	224		264	262
Unpaid claims and claim expenses - U.S. Medical	3,184		$ 2,697	$ 2,420
Incurral Year - 2019
Claims Development [Line Items]
Incurred Costs	23,211	$ 23,306
Unpaid Claims & Claim Expenses	$ 60
Claims Frequency | claim	3.5
Cumulative Costs Paid	$ 23,151	$ 20,920
Outstanding liabilities for the periods presented, net of reinsurance	60
Incurral Year - 2020
Claims Development [Line Items]
Incurred Costs	24,927
Unpaid Claims & Claim Expenses	$ 2,764
Claims Frequency | claim	3.7
Cumulative Costs Paid	$ 22,163
Outstanding liabilities for the periods presented, net of reinsurance	$ 2,764