Fair Value of Assets and Liabilities - Assets and liabilities measured at fair value on a recurring and non-recurring basis (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Assets
Fixed income securities:	$ 66,551	$ 59,044
Equity securities	4,395	8,162
Short-term investments	4,559	4,256
Separate account assets	3,064	3,044
Counterparty and cash collateral netting	$ (25)	$ (40)
% of total assets at fair value	0.00%	(0.10%)
Total	$ 80,470	$ 76,461
Liabilities
Counterparty and cash collateral netting	$ 10	$ 12
Counterparty and cash collateral netting as a percent of liabilities measured at fair value	(1.80%)	(2.20%)
U.S. government and agencies
Assets
Fixed income securities:	$ 2,850	$ 5,086
Municipal
Assets
Fixed income securities:	9,709	8,620
Foreign government
Assets
Fixed income securities:	1,017	979
ABS
Assets
Fixed income securities:	1,206	862
MBS
Assets
Fixed income securities:	92	419
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 13,399	$ 17,081
% of total assets at fair value	17.00%	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	$ 64,473	$ 56,868
% of total assets at fair value	81.90%	76.20%
Liabilities
Total recurring basis liabilities	$ (72)	$ (84)
Liabilities as a percent of liabilities measured at fair value	12.90%	15.70%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 855	$ 738
% of total assets at fair value	1.10%	1.00%
Liabilities
Total recurring basis liabilities	$ (497)	$ (462)
Liabilities as a percent of liabilities measured at fair value	88.90%	86.50%
Investments reported at NAV
Assets
Investments reported at NAV	$ 1,768	$ 1,814
Recurring
Assets
Other investments: Free-standing derivatives, Counterparty and cash collateral netting	(25)	(40)
Liabilities
Counterparty and cash collateral netting	10	12
Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities:	2,480	4,689
Equity securities	3,647	7,407
Short-term investments	4,207	1,940
Other investments: Free-standing derivatives	0	0
Separate account assets	3,064	3,044
Other assets	1	1
Total assets at fair value	13,399	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:	2,480	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:	63,634	54,013
Equity securities	360	384
Short-term investments	322	2,291
Other investments: Free-standing derivatives	157	180
Separate account assets	0	0
Other assets	0	0
Total assets at fair value	64,473	56,868
Liabilities
Other liabilities: Free-standing derivatives	(72)	(84)
Recurring | Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities:	370	397
Recurring | Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities:	9,640	8,558
Recurring | Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities:	37,118	30,819
Recurring | Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities:	14,304	12,084
Recurring | Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities:	1,017	979
Recurring | Significant other observable inputs (Level 2) | ABS
Assets
Fixed income securities:	1,124	797
Recurring | Significant other observable inputs (Level 2) | MBS
Assets
Fixed income securities:	61	379
Recurring | Significant unobservable inputs (Level 3)
Assets
Fixed income securities:	437	342
Equity securities	388	371
Short-term investments	30	25
Other investments: Free-standing derivatives	0	0
Separate account assets	0	0
Other assets		0
Total assets at fair value	855	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:	69	62
Recurring | Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities:	136	61
Recurring | Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities:	119	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	(497)	(462)
Fair value
Assets
Total assets at fair value	$ 78,702	$ 74,647
% of total assets at fair value	100.00%	100.00%
Liabilities
Total recurring basis liabilities	$ (559)	$ (534)
Liabilities as a percent of liabilities measured at fair value	100.00%	100.00%
Fair value | Recurring
Assets
Fixed income securities:	$ 66,551	$ 59,044
Equity securities	4,395	8,162
Short-term investments	4,559	4,256
Other investments: Free-standing derivatives	132	140
Separate account assets	3,064	3,044
Other assets	1	1
Total assets at fair value	78,702	74,647
Liabilities
Other liabilities: Free-standing derivatives	(62)	(72)
Fair value | Recurring | U.S. government and agencies
Assets
Fixed income securities:	2,850	5,086
Fair value | Recurring | Municipal
Assets
Fixed income securities:	9,709	8,620
Fair value | Recurring | Corporate - public
Assets
Fixed income securities:	37,254	30,880
Fair value | Recurring | Corporate - privately placed
Assets
Fixed income securities:	14,423	12,198
Fair value | Recurring | Foreign government
Assets
Fixed income securities:	1,017	979
Fair value | Recurring | ABS
Assets
Fixed income securities:	1,206	862
Fair value | Recurring | MBS
Assets
Fixed income securities:	92	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:	82	65
Fair value | Recurring | Significant unobservable inputs (Level 3) | MBS
Assets
Fixed income securities:	31	40
Fair value | Contractholder funds: Derivatives embedded in life and annuity contracts | Recurring
Liabilities
Contractholder funds: Derivatives embedded in life and annuity contracts	(497)	(462)
Fixed Income Securities Valued Based on Nonbinding Broker Quotes
Assets
Total assets at fair value	126	50
Municipal Not Rated by Third Party Credit Rating Agencies
Assets
Total assets at fair value	$ 34	$ 36