Fair Value of Assets and Liabilities - Assets and liabilities measured at fair value on a recurring and non-recurring basis (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets
Fixed income securities	$ 66,354	$ 59,044
Equity securities	4,710	8,162
Short-term investments	7,800	4,256
Separate account assets	3,344	3,044
Counterparty and cash collateral netting	(15)
Assets at fair value counterparty and cash collateral netting	$ (15)	$ (40)
Assets as a percent of assets measured at fair value	0.00%	(0.10%)
Total	$ 84,237	$ 76,461
Liabilities
Liabilities as a percent of liabilities measured at fair value	(4.20%)	(2.20%)
U.S. government and agencies
Assets
Fixed income securities	$ 3,222	$ 5,086
Municipal
Assets
Fixed income securities	9,587	8,620
Foreign government
Assets
Fixed income securities	1,055	979
ABS
Assets
Fixed income securities	1,270	862
MBS
Assets
Fixed income securities	78	419
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 17,567	$ 17,081
Assets as a percent of assets measured at fair value	21.30%	22.90%
Liabilities
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	$ 64,029	$ 56,868
Assets as a percent of assets measured at fair value	77.70%	76.20%
Liabilities
Liabilities as a percent of liabilities measured at fair value	23.80%	15.70%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 832	$ 738
Assets as a percent of assets measured at fair value	1.00%	1.00%
Liabilities
Liabilities as a percent of liabilities measured at fair value	80.40%	86.50%
Investments reported at NAV
Assets
Investments measured using the net asset value practical expedient	$ 1,824	$ 1,814
Recurring
Assets
Other investments: Free-standing derivatives, Counterparty and cash collateral netting	(15)	(40)
Counterparty and cash collateral netting		(40)
Liabilities
Counterparty and cash collateral netting	27	12
Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities	2,863	4,689
Equity securities	3,882	7,407
Short-term investments	7,477	1,940
Other investments: Free-standing derivatives	0	0
Separate account assets	3,344	3,044
Other assets	1	1
Total assets at fair value		17,081
Liabilities
Other liabilities: Free-standing derivatives	0	0
Total liabilities at fair value	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | Contractholder funds: Derivatives embedded in life and annuity contracts
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | U.S. government and agencies
Assets
Fixed income securities	2,863	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	63,112	54,013
Equity securities	410	384
Short-term investments	288	2,291
Other investments: Free-standing derivatives	219	180
Separate account assets	0	0
Other assets	0	0
Total assets at fair value		56,868
Liabilities
Other liabilities: Free-standing derivatives	(153)	(84)
Total liabilities at fair value	(153)	(84)
Recurring | Significant other observable inputs (Level 2) | Contractholder funds: Derivatives embedded in life and annuity contracts
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	0	0
Recurring | Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities	359	397
Recurring | Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities	9,520	8,558
Recurring | Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities	36,346	30,819
Recurring | Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities	14,568	12,084
Recurring | Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities	1,055	979
Recurring | Significant other observable inputs (Level 2) | ABS
Assets
Fixed income securities	1,213	797
Recurring | Significant other observable inputs (Level 2) | MBS
Assets
Fixed income securities	51	379
Recurring | Significant unobservable inputs (Level 3)
Assets
Fixed income securities	379	342
Equity securities	418	371
Short-term investments	35	25
Other investments: Free-standing derivatives	0	0
Separate account assets	0	0
Other assets	0	0
Total assets at fair value		738
Liabilities
Other liabilities: Free-standing derivatives	0	0
Total liabilities at fair value	(516)	(462)
Recurring | Significant unobservable inputs (Level 3) | Contractholder funds: Derivatives embedded in life and annuity contracts
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(516)	(462)
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	67	62
Recurring | Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities	98	61
Recurring | Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities	130	114
Recurring | Significant unobservable inputs (Level 3) | Foreign government
Assets
Fixed income securities		0
Fair value
Assets
Total assets at fair value	$ 82,413	$ 74,647
Assets as a percent of assets measured at fair value	100.00%	100.00%
Liabilities
Liabilities as a percent of liabilities measured at fair value	100.00%	100.00%
Fair value | Recurring
Assets
Fixed income securities	$ 66,354	$ 59,044
Equity securities	4,710	8,162
Short-term investments	7,800	4,256
Other investments: Free-standing derivatives	204	140
Separate account assets	3,344	3,044
Other assets	1	1
Total assets at fair value		74,647
Liabilities
Other liabilities: Free-standing derivatives	(126)	(72)
Total liabilities at fair value	(642)	(534)
Fair value | Recurring | Contractholder funds: Derivatives embedded in life and annuity contracts
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(516)	(462)
Fair value | Recurring | U.S. government and agencies
Assets
Fixed income securities	3,222	5,086
Fair value | Recurring | Municipal
Assets
Fixed income securities	9,587	8,620
Fair value | Recurring | Corporate - public
Assets
Fixed income securities	36,444	30,880
Fair value | Recurring | Corporate - privately placed
Assets
Fixed income securities	14,698	12,198
Fair value | Recurring | Foreign government
Assets
Fixed income securities	1,055	979
Fair value | Recurring | ABS
Assets
Fixed income securities	1,270	862
Fair value | Recurring | MBS
Assets
Fixed income securities	78	419
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	57	65
Fair value | Recurring | Significant unobservable inputs (Level 3) | MBS
Assets
Fixed income securities	$ 27	$ 40