Insurance and Contractholder Liabilities - Summary of Insurance and Contractholder Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current
Contractholder deposit funds	$ 350
Future policy benefits	327
Unearned premiums	485
Contractholder deposit funds		$ 600
Future policy benefits		553
Unearned premiums		453
Total		7,010
Insurance and contractholder liabilities classified as held for sale		(2,089)
Total insurance and contractholder liabilities	5,308	4,921
Non-current
Contractholder deposit funds	6,823
Future policy benefits	9,317
Unearned premiums	394
Contractholder deposit funds		7,139
Future policy benefits		9,281
Unearned premiums		360
Total		20,271
Insurance and contractholder liabilities classified as held for sale		(4,219)
Total insurance and contractholder liabilities	16,844	16,052
Total
Contractholder deposit funds	7,173
Future policy benefits	9,644
Unearned premiums	879
Contractholder deposit funds		7,739
Future policy benefits		9,834
Unearned premiums		813
Total		27,281
Insurance and contractholder liabilities classified as held for sale		(6,308)
Total insurance and contractholder liabilities	22,152	20,973
Unpaid claims classified as liabilities of business held for sale		4,900
Contractholder deposit funds classified as liabilities of business held for sale		717
Future policy benefits classified as liabilities of business held for sale		653
U.S. Medical
Current
Unpaid claims and claim expenses	3,166
Unpaid claims and claim expenses		2,875
Non-current
Unpaid claims and claim expenses	18
Unpaid claims and claim expenses		17
Total
Unpaid claims and claim expenses	3,184		$ 2,697	$ 2,420
Unpaid claims and claim expenses		2,892
Other segments
Current
Unpaid claims and claim expenses	980
Unpaid claims and claim expenses		2,529
Non-current
Unpaid claims and claim expenses	292
Unpaid claims and claim expenses		3,474
Total
Unpaid claims and claim expenses	$ 1,272
Unpaid claims and claim expenses		$ 6,003