Insurance and Contractholder Liabilities - Integrated Medical - Unpaid Claims Development (Details) - Integrated Medical [Member] Claims in Millions, $ in Millions	Dec. 31, 2018 USD ($) Claims	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Claims Development [Line Items]
Incurred claims	$ 38,986
Cumulative Paid Claims	36,698
Outstanding liabilities for the periods presented, net of reinsurance	2,288
Other long-duration liabilities not included in development table above	145
Liability for unpaid claims and claims expenses, net of reinsurance	2,433	$ 2,158	$ 1,988	$ 1,868
Reinsurance recoverable on unpaid claims	264	262	273	237
Total liability for unpaid claims and claims expenses	$ 2,697	2,420	$ 2,261	$ 2,105
Percent of health claims paid within one year	95.00%
Minimum [Member]
Claims Development [Line Items]
Percent of health claims paid within one year	95.00%
Accident Year 2017 [Member]
Claims Development [Line Items]
Incurred claims	$ 18,528	18,692
Cumulative Paid Claims	18,506	$ 16,628
Liability for unpaid claims and claims expenses, net of reinsurance	$ 22
Claim frequency | Claims	2.6
Accident Year 2018 [Member]
Claims Development [Line Items]
Incurred claims	$ 20,458
Cumulative Paid Claims	18,192
Liability for unpaid claims and claims expenses, net of reinsurance	$ 2,266
Claim frequency | Claims	2.9