Related party transactions (Schedule of related party transactions) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Related Party Transaction [Line Items]
Ceded Premiums Written	$ 10,258	$ 8,912	$ 7,441
Losses and loss expenses	23,342	21,980	21,710
Insurance and reinsurance balances payable	7,795	7,243
Other (income) expense	74	(2,365)	(994)
Other Investments	$ 13,696	$ 11,169
Bermuda \| ABR Reinsurance Capital Holdings Ltd. [Member]
Related Party Transaction [Line Items]
Ownership Percentage	19.00%	17.00%
Bermuda \| ABR Reinsurance Capital Holdings Ltd. [Member] \| ABR Reinsurance Capital Holdings Ltd. [Member]
Related Party Transaction [Line Items]
Ownership Percentage	18.80%
Starr Technical Risk Agency and Affiliates [Member]
Related Party Transaction [Line Items]
Minimum Amount of Program Business to be Written to Earn Profit Sharing	$ 20
Premiums Written, Gross	618	$ 592	507
Ceded Premiums Written	353	321	253
Paid commissions	122	114	97
Commissions received	79	73	59
Losses and loss expenses	225	157	170
Reinsurance Recoverable on Losses and Loss Expenses	541	516
Insurance and reinsurance balances payable	96	88
ABR Reinsurance Capital Holdings Ltd. [Member]
Related Party Transaction [Line Items]
Ceded Premiums Written	507	442	350
Commissions received	138	133	100
Reinsurance Recoverable on Losses and Loss Expenses	1,050	963
Insurance and reinsurance balances payable	$ 110	107
Warrants & Rights Outstanding	0.50%
BlackRock, Inc.
Related Party Transaction [Line Items]
Revenue from Related Parties	$ 7	11	3
Aquiline Capital Partners LLC
Related Party Transaction [Line Items]
Investment Company, Financial Commitment to Investee, Future Amount	267
Other (income) expense	8	68	$ 2
Other Investments	$ 271	$ 245

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Reinsurance Recoverable on Losses and Loss Expenses

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