Insurance and Contractholder Liabilities - Summary of Insurance and Contractholder Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Current
Contractholder deposit funds	$ 624	$ 600
Future policy benefits	597	553
Unearned premiums, current	449	453
Total	7,373	7,010
Insurance and contractholder liabilities classified as held for sale	(2,150)	(2,089)
Total insurance and contractholder liabilities	5,223	4,921
Non-current
Contractholder deposit funds	7,038	7,139
Future policy benefits	9,505	9,281
Unearned premiums	379	360
Total	20,654	20,271
Insurance and contractholder liabilities classified as held for sale	(4,441)	(4,219)
Total insurance and contractholder liabilities	16,213	16,052
Total
Contractholder deposit funds	7,662	7,739
Future policy benefits	10,102	9,834
Unearned premiums	828	813
Total	28,027	27,281
Insurance and contractholder liabilities classified as held for sale	(6,591)	(6,308)
Contractholder deposit funds			$ 7,789
Future policy benefits			9,808
Unearned premiums			755
Total insurance and contractholder liabilities	21,436	20,973	27,270
Unpaid claims classified as liabilities of business held for sale	5,200	4,900
Contractholder deposit funds classified as liabilities of business held for sale	759	717
Future policy benefits classified as liabilities of business held for sale	646	653
U.S. Medical
Current
Unpaid claims and claim expenses	3,182	2,875
Non-current
Unpaid claims and claim expenses	18	17
Total
Unpaid claims and claim expenses	3,200	2,892
Unpaid claims and claim expenses			3,061	$ 2,697
Other segments
Current
Unpaid claims and claim expenses	2,521	2,529
Non-current
Unpaid claims and claim expenses	3,714	3,474
Total
Unpaid claims and claim expenses	$ 6,235	$ 6,003
Unpaid claims and claim expenses			$ 5,857