Fair Value of Assets and Liabilities - Assets and liabilities measured at fair value on a recurring and non-recurring basis (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Assets
Fixed income securities:	$ 64,448	$ 59,044
Equity securities	4,212	8,162
Short-term investments	5,344	4,256
Separate account assets	2,906	3,044
Counterparty and cash collateral netting	$ (43)	$ (40)
% of total assets at fair value	0.00%	(0.10%)
Total	$ 78,763	$ 76,461
Liabilities
Counterparty and cash collateral netting	$ 8	$ 12
Counterparty and cash collateral netting as a percent of liabilities measured at fair value	(1.40%)	(2.20%)
U.S. government and agencies
Assets
Fixed income securities:	$ 3,519	$ 5,086
Municipal
Assets
Fixed income securities:	9,285	8,620
Foreign government
Assets
Fixed income securities:	961	979
ABS
Assets
Fixed income securities:	759	862
MBS
Assets
Fixed income securities:	184	419
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 14,442	$ 17,081
% of total assets at fair value	18.70%	22.90%
Liabilities
Total recurring basis liabilities	$ 0	$ 0
Liabilities as a percent of liabilities measured at fair value	0.00%	0.00%
Significant other observable inputs (Level 2)
Assets
Total assets at fair value	$ 61,925	$ 56,868
% of total assets at fair value	80.30%	76.20%
Liabilities
Total recurring basis liabilities	$ (109)	$ (84)
Liabilities as a percent of liabilities measured at fair value	18.50%	15.70%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 774	$ 738
% of total assets at fair value	1.00%	1.00%
Liabilities
Total recurring basis liabilities	$ (488)	$ (462)
Liabilities as a percent of liabilities measured at fair value	82.90%	86.50%
Investments reported at NAV
Assets
Investments reported at NAV	$ 1,665	$ 1,814
Recurring
Assets
Other investments: Free-standing derivatives, Counterparty and cash collateral netting	(43)	(40)
Liabilities
Counterparty and cash collateral netting	8	12
Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities:	3,146	4,689
Equity securities	3,481	7,407
Short-term investments	4,907	1,940
Other investments: Free-standing derivatives	0	0
Separate account assets	2,906	3,044
Other assets	2	1
Total assets at fair value	14,442	17,081
Liabilities
Other liabilities: Free-standing derivatives	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | U.S. government and agencies
Assets
Fixed income securities:	3,146	4,689
Recurring | Quoted prices in active markets for identical assets (Level 1) | Municipal
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate - public
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Corporate - privately placed
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Foreign government
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | ABS
Assets
Fixed income securities:	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | MBS
Assets
Fixed income securities:	0	0
Recurring | Significant other observable inputs (Level 2)
Assets
Fixed income securities:	60,931	54,013
Equity securities	338	384
Short-term investments	427	2,291
Other investments: Free-standing derivatives	229	180
Separate account assets	0	0
Other assets	0	0
Total assets at fair value	61,925	56,868
Liabilities
Other liabilities: Free-standing derivatives	(109)	(84)
Recurring | Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities:	373	397
Recurring | Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities:	9,202	8,558
Recurring | Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities:	35,944	30,819
Recurring | Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities:	13,603	12,084
Recurring | Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities:	961	979
Recurring | Significant other observable inputs (Level 2) | ABS
Assets
Fixed income securities:	709	797
Recurring | Significant other observable inputs (Level 2) | MBS
Assets
Fixed income securities:	139	379
Recurring | Significant unobservable inputs (Level 3)
Assets
Fixed income securities:	371	342
Equity securities	393	371
Short-term investments	10	25
Other investments: Free-standing derivatives	0	0
Separate account assets	0	0
Other assets		0
Total assets at fair value	774	738
Liabilities
Other liabilities: Free-standing derivatives	0	0
Recurring | Significant unobservable inputs (Level 3) | U.S. government and agencies
Assets
Fixed income securities:	0	0
Recurring | Significant unobservable inputs (Level 3) | Municipal
Assets
Fixed income securities:	83	62
Recurring | Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities:	67	61
Recurring | Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities:	126	114
Recurring | Significant unobservable inputs (Level 3) | Foreign government
Assets
Fixed income securities:		0
Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring | Quoted prices in active markets for identical assets (Level 1)
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring | Significant other observable inputs (Level 2)
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring | Significant unobservable inputs (Level 3)
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(488)	(462)
Fair value
Assets
Total assets at fair value	$ 77,098	$ 74,647
% of total assets at fair value	100.00%	100.00%
Liabilities
Total recurring basis liabilities	$ (589)	$ (534)
Liabilities as a percent of liabilities measured at fair value	100.00%	100.00%
Fair value | Recurring
Assets
Fixed income securities:	$ 64,448	$ 59,044
Equity securities	4,212	8,162
Short-term investments	5,344	4,256
Other investments: Free-standing derivatives	186	140
Separate account assets	2,906	3,044
Other assets	2	1
Total assets at fair value	77,098	74,647
Liabilities
Other liabilities: Free-standing derivatives	(101)	(72)
Fair value | Recurring | U.S. government and agencies
Assets
Fixed income securities:	3,519	5,086
Fair value | Recurring | Municipal
Assets
Fixed income securities:	9,285	8,620
Fair value | Recurring | Corporate - public
Assets
Fixed income securities:	36,011	30,880
Fair value | Recurring | Corporate - privately placed
Assets
Fixed income securities:	13,729	12,198
Fair value | Recurring | Foreign government
Assets
Fixed income securities:	961	979
Fair value | Recurring | ABS
Assets
Fixed income securities:	759	862
Fair value | Recurring | MBS
Assets
Fixed income securities:	184	419
Fair value | Recurring | Significant unobservable inputs (Level 3)
Assets
Other assets	0
Fair value | Recurring | Significant unobservable inputs (Level 3) | Foreign government
Assets
Fixed income securities:	0
Fair value | Recurring | Significant unobservable inputs (Level 3) | ABS
Assets
Fixed income securities:	50	65
Fair value | Recurring | Significant unobservable inputs (Level 3) | MBS
Assets
Fixed income securities:	45	40
Fair value | Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(488)	(462)
Fixed Income Securities Valued Based on Nonbinding Broker Quotes
Assets
Total assets at fair value	116	50
Municipal Not Rated by Third Party Credit Rating Agencies
Assets
Total assets at fair value	$ 35	$ 36