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, 2021	Dec. 31, 2020
Assets
Fixed income securities	$ 42,136	$ 42,565
Equity securities	7,061	3,168
Short-term investments	4,009	6,807
Assets held for sale	0	42,131
Total assets at fair value	53,318	82,413
Assets at fair value counterparty and cash collateral netting	$ (22)	$ (15)
Assets as a percent of assets measured at fair value	0.00%	0.00%
Total	$ 54,849	$ 84,237
Liabilities
Other liabilities	(401)	(306)
Liabilities held for sale	$ 0	$ (33,325)
Liabilities as a percent of liabilities measured at fair value	(87.50%)	(4.20%)
U.S. government and agencies
Assets
Fixed income securities	$ 6,273	$ 2,107
Municipal
Assets
Fixed income securities	6,393	7,578
Foreign government
Assets
Fixed income securities	985	958
ABS
Assets
Fixed income securities	1,155	905
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 13,700	$ 17,567
Assets as a percent of assets measured at fair value	25.70%	21.30%
Liabilities
Liabilities as a percent of liabilities measured at fair value	37.50%	0.00%
Significant other observable inputs (Level 2)
Assets
Total assets at fair value	$ 39,043	$ 64,029
Assets as a percent of assets measured at fair value	73.20%	77.70%
Liabilities
Liabilities as a percent of liabilities measured at fair value	150.00%	23.80%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 597	$ 832
Assets as a percent of assets measured at fair value	1.10%	1.00%
Liabilities
Liabilities as a percent of liabilities measured at fair value	0.00%	80.40%
Reported at NAV
Assets
Assets held for sale		$ 762
Investments measured using the net asset value practical expedient	$ 1,531	1,062
Recurring
Assets
Fixed income securities	42,136	42,565
Equity securities	7,061	3,168
Short-term investments	4,009	6,807
Other investments	14	20
Other investments, Counterparty and cash collateral netting	(22)	(9)
Other assets	66	1
Assets held for sale		29,852
Assets held for sale, Counterparty and cash collateral netting		(6)
Total assets at fair value	53,286	82,413
Assets at fair value counterparty and cash collateral netting	(22)	(15)
Liabilities
Other liabilities	(8)	(16)
Other liabilities, Counterparty and cash collateral netting	7	18
Liabilities held for sale		(626)
Liabilities held for sale, Counterparty and cash collateral netting		9
Total liabilities at fair value	(8)	(642)
Counterparty and cash collateral netting	7	27
Recurring | U.S. government and agencies
Assets
Fixed income securities	6,273	2,106
Recurring | Municipal
Assets
Fixed income securities	6,393	7,579
Recurring | Corporate - public
Assets
Fixed income securities	16,589	21,952
Recurring | Corporate - privately placed
Assets
Fixed income securities	10,741	9,065
Recurring | Foreign government
Assets
Fixed income securities	985	958
Recurring | ABS
Assets
Fixed income securities	1,155	905
Recurring | Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities	6,247	2,061
Equity securities	6,312	2,468
Short-term investments	1,140	6,549
Other investments	0	0
Other assets	1	1
Assets held for sale		6,488
Total assets at fair value	13,700	17,567
Liabilities
Other liabilities	(3)	0
Liabilities held for sale		0
Total liabilities at fair value	(3)	0
Recurring | Quoted prices in active markets for identical assets (Level 1) | U.S. government and agencies
Assets
Fixed income securities	6,247	2,061
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 | Significant other observable inputs (Level 2)
Assets
Fixed income securities	35,745	40,278
Equity securities	400	396
Short-term investments	2,864	223
Other investments	34	29
Other assets	0	0
Assets held for sale		23,103
Total assets at fair value	39,043	64,029
Liabilities
Other liabilities	(12)	(34)
Liabilities held for sale		(119)
Total liabilities at fair value	(12)	(153)
Recurring | Significant other observable inputs (Level 2) | U.S. government and agencies
Assets
Fixed income securities	26	45
Recurring | Significant other observable inputs (Level 2) | Municipal
Assets
Fixed income securities	6,375	7,562
Recurring | Significant other observable inputs (Level 2) | Corporate - public
Assets
Fixed income securities	16,569	21,885
Recurring | Significant other observable inputs (Level 2) | Corporate - privately placed
Assets
Fixed income securities	10,675	9,002
Recurring | Significant other observable inputs (Level 2) | Foreign government
Assets
Fixed income securities	985	958
Recurring | Significant other observable inputs (Level 2) | ABS
Assets
Fixed income securities	1,115	826
Recurring | Significant unobservable inputs (Level 3)
Assets
Fixed income securities	144	226
Equity securities	349	304
Short-term investments	5	35
Other investments	2	0
Other assets	65	0
Assets held for sale		267
Total assets at fair value	565	832
Liabilities
Other liabilities	0	0
Liabilities held for sale		(516)
Total liabilities at fair value	0	(516)
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	18	17
Recurring | Significant unobservable inputs (Level 3) | Corporate - public
Assets
Fixed income securities	20	67
Recurring | Significant unobservable inputs (Level 3) | Corporate - privately placed
Assets
Fixed income securities	66	63
Recurring | Significant unobservable inputs (Level 3) | Foreign government
Assets
Fixed income securities	0	0
Recurring | Significant unobservable inputs (Level 3) | ABS
Assets
Fixed income securities	40	$ 79
Non-recurring basis
Assets
Total assets at fair value	32
Non-recurring basis | Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	0
Non-recurring basis | Significant other observable inputs (Level 2)
Assets
Total assets at fair value	0
Non-recurring basis | Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 32
Fair value
Assets
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 | Significant unobservable inputs (Level 3)
Assets
Assets held for sale	$ 0	$ 4,440
Liabilities
Liabilities held for sale	$ 0	$ (9,424)