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, 2022	Dec. 31, 2021
Assets
Fixed income securities	$ 42,485	$ 42,136
Equity securities	4,567	7,061
Short-term investments	4,173	4,009
Other investments	1,728	2,656
Total assets at fair value	51,358	53,318
Counterparty and cash collateral netting	$ (22)	$ (22)
% of total assets at fair value	0.00%	0.00%
Total	$ 52,604	$ 54,849
Liabilities
Other liabilities	$ (371)	$ (401)
% of total liabilities at fair value	(420.00%)	(87.50%)
Fair value
Assets
% of total assets at fair value	100.00%	100.00%
Liabilities
% of total liabilities at fair value	100.00%	100.00%
U.S. government and agencies
Assets
Fixed income securities	$ 7,898	$ 6,273
Municipal
Assets
Fixed income securities	6,210	6,393
Foreign government
Assets
Fixed income securities	957	985
ABS
Assets
Fixed income securities	1,157	1,155
Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	$ 12,325	$ 13,700
% of total assets at fair value	24.00%	25.70%
Liabilities
% of total liabilities at fair value	20.00%	37.50%
Significant other observable inputs (Level 2)
Assets
Total assets at fair value	$ 38,414	$ 39,043
% of total assets at fair value	74.80%	73.20%
Liabilities
% of total liabilities at fair value	500.00%	150.00%
Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 641	$ 597
% of total assets at fair value	1.20%	1.10%
Liabilities
% of total liabilities at fair value	0.00%	0.00%
Reported at NAV
Assets
Investments reported at NAV	$ 1,246	$ 1,531
Recurring basis
Assets
Fixed income securities	42,485	42,136
Equity securities	4,567	7,061
Short-term investments	4,173	4,009
Other investments	4	14
Other investments	22	22
Other assets	106	66
Total assets at fair value	51,335	53,286
Counterparty and cash collateral netting	(22)	(22)
Liabilities
Other liabilities	(5)	(8)
Other liabilities	21	7
Total recurring basis liabilities	(5)	(8)
Counterparty and cash collateral netting	21	7
Recurring basis \| U.S. government and agencies
Assets
Fixed income securities	7,898	6,273
Recurring basis \| Municipal
Assets
Fixed income securities	6,210	6,393
Recurring basis \| Corporate - public
Assets
Fixed income securities	18,616	16,589
Recurring basis \| Corporate - privately placed
Assets
Fixed income securities	7,647	10,741
Recurring basis \| Foreign government
Assets
Fixed income securities	957	985
Recurring basis \| ABS
Assets
Fixed income securities	1,157	1,155
Recurring basis \| Quoted prices in active markets for identical assets (Level 1)
Assets
Fixed income securities	7,878	6,247
Equity securities	3,936	6,312
Short-term investments	508	1,140
Other investments	0	0
Other assets	3	1
Total assets at fair value	12,325	13,700
Liabilities
Other liabilities	(1)	(3)
Total recurring basis liabilities	(1)	(3)
Recurring basis \| Quoted prices in active markets for identical assets (Level 1) \| U.S. government and agencies
Assets
Fixed income securities	7,878	6,247
Recurring basis \| Quoted prices in active markets for identical assets (Level 1) \| Municipal
Assets
Fixed income securities	0	0
Recurring basis \| Quoted prices in active markets for identical assets (Level 1) \| Corporate - public
Assets
Fixed income securities	0	0
Recurring basis \| Quoted prices in active markets for identical assets (Level 1) \| Corporate - privately placed
Assets
Fixed income securities	0	0
Recurring basis \| Quoted prices in active markets for identical assets (Level 1) \| Foreign government
Assets
Fixed income securities	0	0
Recurring basis \| Quoted prices in active markets for identical assets (Level 1) \| ABS
Assets
Fixed income securities	0	0
Recurring basis \| Significant other observable inputs (Level 2)
Assets
Fixed income securities	34,434	35,745
Equity securities	298	400
Short-term investments	3,659	2,864
Other investments	23	34
Other assets	0	0
Total assets at fair value	38,414	39,043
Liabilities
Other liabilities	(25)	(12)
Total recurring basis liabilities	(25)	(12)
Recurring basis \| Significant other observable inputs (Level 2) \| U.S. government and agencies
Assets
Fixed income securities	20	26
Recurring basis \| Significant other observable inputs (Level 2) \| Municipal
Assets
Fixed income securities	6,189	6,375
Recurring basis \| Significant other observable inputs (Level 2) \| Corporate - public
Assets
Fixed income securities	18,547	16,569
Recurring basis \| Significant other observable inputs (Level 2) \| Corporate - privately placed
Assets
Fixed income securities	7,592	10,675
Recurring basis \| Significant other observable inputs (Level 2) \| Foreign government
Assets
Fixed income securities	957	985
Recurring basis \| Significant other observable inputs (Level 2) \| ABS
Assets
Fixed income securities	1,129	1,115
Recurring basis \| Significant unobservable inputs (Level 3)
Assets
Fixed income securities	173	144
Equity securities	333	349
Short-term investments	6	5
Other investments	3	2
Other assets	103	65
Total assets at fair value	618	565
Liabilities
Other liabilities	0	0
Total recurring basis liabilities	0	0
Recurring basis \| Significant unobservable inputs (Level 3) \| U.S. government and agencies
Assets
Fixed income securities	0	0
Recurring basis \| Significant unobservable inputs (Level 3) \| Municipal
Assets
Fixed income securities	21	18
Recurring basis \| Significant unobservable inputs (Level 3) \| Corporate - public
Assets
Fixed income securities	69	20
Recurring basis \| Significant unobservable inputs (Level 3) \| Corporate - privately placed
Assets
Fixed income securities	55	66
Recurring basis \| Significant unobservable inputs (Level 3) \| Foreign government
Assets
Fixed income securities	0	0
Recurring basis \| Significant unobservable inputs (Level 3) \| ABS
Assets
Fixed income securities	28	40
Non-recurring basis
Assets
Total assets at fair value	23	32
Non-recurring basis \| Quoted prices in active markets for identical assets (Level 1)
Assets
Total assets at fair value	0	0
Non-recurring basis \| Significant other observable inputs (Level 2)
Assets
Total assets at fair value	0	0
Non-recurring basis \| Significant unobservable inputs (Level 3)
Assets
Total assets at fair value	$ 23	$ 32

Assets as a percent of total assets measured at fair value on a recurring and non-recurring basis.

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Liabilities as a percent of total liabilities measured at fair value on a recurring and non-recurring basis.

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Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial and nonfinancial obligations.

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