Insurance and Contractholder Liabilities - Summary of Insurance and Contractholder Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Current
Contractholder deposit funds	$ 613	$ 600
Future policy benefits	541	553
Unearned premiums, current	480	453
Total	7,160	7,010
Insurance and contractholder liabilities classified as held for sale	(2,130)	(2,089)
Total insurance and contractholder liabilities	5,030	4,921
Non-current
Contractholder deposit funds	7,086	7,139
Future policy benefits	9,110	9,281
Unearned premiums	360	360
Total	20,149	20,271
Insurance and contractholder liabilities classified as held for sale	(4,311)	(4,219)
Total insurance and contractholder liabilities	15,838	16,052
Total
Contractholder deposit funds	7,699	7,739
Future policy benefits	9,651	9,834
Unearned premiums	840	813
Total	27,309	27,281
Insurance and contractholder liabilities classified as held for sale	(6,441)	(6,308)
Contractholder deposit funds			$ 7,947
Future policy benefits			9,691
Unearned premiums			779
Total insurance and contractholder liabilities	20,868	20,973	27,103
Unpaid claims	5,100	4,900
Contractholder deposit funds	726	717
Future policy benefits	640	653
Integrated Medical
Current
Unpaid claims and claim expenses	2,982	2,875
Non-current
Unpaid claims and claim expenses	18	17
Total
Unpaid claims and claim expenses	3,000	2,892
Unpaid claims and claim expenses			2,961	$ 2,697
Other segments
Current
Unpaid claims and claim expenses	2,544	2,529
Non-current
Unpaid claims and claim expenses	3,575	3,474
Total
Unpaid claims and claim expenses	$ 6,119	$ 6,003
Unpaid claims and claim expenses			$ 5,725