Insurance and Contractholder Liabilities - Account Balances (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Insurance and Contractholder Liabilities [Line Items]
Contractholder deposit funds, current		$ 641
Future policy benefits, current		740
Unearned premiums, current		348
Total insurance and contractholder liabilities, current	$ 4,921	6,801
Contractholder deposit funds, non-current		7,365
Future policy benefits, non-current		8,981
Unearned premiums, non-current		379
Total insurance and contractholder liabilities, non-current	16,052	19,974
Contractholder deposit funds		8,006
Future policy benefits		9,721
Unearned premiums		727
Total insurance and contractholder liabilities	$ 20,973	26,775
Maximum [Member]
Insurance and Contractholder Liabilities [Line Items]
Interest rate assumptions for Future policy benefits obligations	9.00%
Minimum [Member]
Insurance and Contractholder Liabilities [Line Items]
Interest rate assumptions for Future policy benefits obligations	1.00%
Integrated Medical [Member]
Insurance and Contractholder Liabilities [Line Items]
Unpaid claims and claim expenses, current		2,678
Unpaid claims and claim expenses, non-current		19
Total liability for unpaid claims and claims expenses		2,697	$ 2,420	$ 2,261
Other Segments [Member]
Insurance and Contractholder Liabilities [Line Items]
Unpaid claims and claim expenses, current		2,394
Unpaid claims and claim expenses, non-current		3,230
Total liability for unpaid claims and claims expenses		$ 5,624