Insurance and Contractholder Liabilities - Account Balances Including Disposal Groups (Details) $ in Millions	Dec. 31, 2019 USD ($)
Insuarance And Contractholder Liabilities Including Disposal Groups [Abstract]
Contractholder deposit funds, current, including disposal groups	$ 600
Future policy benefits, current, including disposal groups	553
Unearned premiums, current, including disposal groups	453
Total insurance and contractholder liabilities, current, including disposal groups	7,010
Contractholder deposit funds, non-current, including disposal groups	7,139
Future policy benefits, non-current, including disposal groups	9,281
Unearned premiums, non-current, including disposal groups	360
Total insurance and contractholder liabilities, non-current, including disposal groups	20,271
Contractholder deposit funds, including disposal groups	7,739
Future policy benefits, including disposal groups	9,834
Unearned premiums, including disposal groups	813
Total insurance and contractholder liabilities, including disposal groups	27,281
Amounts classified as held for sale:
Unpaid claims classified as held for sale	4,900
Contractholder deposit funds classified as held for sale	717
Future policy benefits classified as held for sale	653
Integrated Medical [Member]
Insuarance And Contractholder Liabilities Including Disposal Groups [Abstract]
Unpaid claims and claim expenses, current, including disposal groups	2,875
Unpaid claims and claim expenses, non-current, including disposal groups	17
Total liability for unpaid claims and claims expenses, including disposal groups	2,892
Other Segments [Member]
Insuarance And Contractholder Liabilities Including Disposal Groups [Abstract]
Unpaid claims and claim expenses, current, including disposal groups	2,529
Unpaid claims and claim expenses, non-current, including disposal groups	3,474
Total liability for unpaid claims and claims expenses, including disposal groups	$ 6,003