Reinsurance and Indemnification - Catastrophe reinsurance (Narrative) (Details) - Catastrophe Reinsurance Program $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) reinstatement contract
Ceded Credit Risk [Line Items]
Catastrophe reinsurance loss amount	$ 2,500
Catastrophe reinsurance aggregate loss limit	6,920
Minimum
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	500
Maximum
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	750
Traditional Market
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	4,690
Catastrophe reinsurance loss limits per contract year	3,580
Exhausting loss from catastrophes	$ 4,250
Number of reinstatements each year for each contract | reinstatement	1
Traditional Market, Placement One | Coverage - I | Four Contracts
Ceded Credit Risk [Line Items]
Exhausting loss from catastrophes	$ 500
Catastrophe annual reinstatement of limits, percentage	31.60%
Contracts number | contract	4
Traditional Market, Placement One | Coverage - II | Five Contracts
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	$ 250
Catastrophe annual reinstatement of limits, percentage	31.70%
Contracts number | contract	5
Catastrophe annual reinstatement of limits	$ 500
Traditional Market, Placement One | Coverage - III | Four Contracts
Ceded Credit Risk [Line Items]
Exhausting loss from catastrophes	$ 1,000
Contracts number | contract	4
Traditional Market, Placement One | Coverage - III | One Contract
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	$ 250
Catastrophe annual reinstatement of limits, percentage	31.70%
Contracts number | contract	1
Catastrophe annual reinstatement of limits	$ 750
Term of catastrophe reinsurance agreement contract	1 year
Traditional Market, Placement One | Coverage - IV | Three Contracts
Ceded Credit Risk [Line Items]
Catastrophe annual reinstatement of limits, percentage	4.00%
Contracts number | contract	3
Term of catastrophe reinsurance agreement contract	1 year
Traditional Market, Placement One | Coverage - V | Two Contracts
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	$ 4,250
Limit of aggregate losses under aggregate excess agreement	$ 500
Catastrophe annual reinstatement of limits, percentage	95.00%
Contracts number | contract	2
Term of catastrophe reinsurance agreement contract	1 year
Traditional Market, Placement One | Minimum | Coverage - IV | Three Contracts
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	$ 1,750
Traditional Market, Placement One | Maximum | Coverage - IV | Three Contracts
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	4,250
Traditional Market, Placement Two
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	4,750
Limit of aggregate losses under aggregate excess agreement	$ 105
Percentage of co-participation	5.00%
Number of reinstatements each year for each contract | reinstatement	1
Term of catastrophe reinsurance agreement contract	8 years
Traditional Market, Placement Two | Coverage - V | Two Contracts
Ceded Credit Risk [Line Items]
Catastrophe annual reinstatement of limits, percentage	4.00%
Traditional Market, Placement Three
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	$ 5,540
Limit of aggregate losses under aggregate excess agreement	$ 131
Percentage of co-participation	5.00%
Number of reinstatements each year for each contract | reinstatement	1
Traditional Market, Placement Four
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	$ 375
Traditional Market, Placement Four | First Contract
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	4,750
Limit of aggregate losses under aggregate excess agreement	$ 95
Contracts number | contract	1
Number of reinstatements each year for each contract | reinstatement	2
Traditional Market, Placement Four | Second Contract
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	$ 4,750
Limit of aggregate losses under aggregate excess agreement	$ 260
Contracts number | contract	1
Number of reinstatements each year for each contract | reinstatement	0
Traditional Market, Placement Four | Third Contract
Ceded Credit Risk [Line Items]
Retention amount for catastrophe reinsurance agreement contracts	$ 6,820
Limit of aggregate losses under aggregate excess agreement	$ 20
Contracts number | contract	1
Number of reinstatements each year for each contract | reinstatement	0
Insurance Linked Securities (ILS)
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	$ 1,800
Insurance Linked Securities (ILS) | Six Contracts
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	$ 1,050
Contracts number | contract	6
Insurance Linked Securities (ILS) | Three Contracts
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	$ 425
Contracts number | contract	3
Insurance Linked Securities (ILS) | Two Contracts
Ceded Credit Risk [Line Items]
Limit of aggregate losses under aggregate excess agreement	$ 325
Contracts number | contract	2