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- Definition

Investment Funds

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Restricted assets.

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No definition available.

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- Definition

Amount of increase (decrease) in allowance for credit loss 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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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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This element represents the aggregate cost of investments accounted for under the equity method of accounting.

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Amount of income (loss) for proportionate share of equity method investee's income (loss).

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- Definition

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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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

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- Definition

Amount of investments classified as other.

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- Definition

The net cash outflow or inflow associated with the acquisition or sale of a business segment during the period.

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No definition available.

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- Definition

The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Investments - Additional Information (Narrative) (Details)	1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($)	Sep. 30, 2024 USD ($) security	Sep. 30, 2023 USD ($)	Jun. 30, 2024 USD ($)	Sep. 30, 2024 USD ($) security	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($)	Sep. 30, 2024 GBP (£) security	Dec. 31, 2023 GBP (£) security	Aug. 31, 2023 GBP (£)	May 05, 2022 USD ($)	Apr. 01, 2022 USD ($)	Sep. 30, 2021 USD ($)	Apr. 01, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 23, 2019 USD ($)	Dec. 20, 2017 USD ($)	Jan. 01, 2017 USD ($)
Gain (Loss) on Securities [Line Items]
Catastrophe bonds, trading, cost		$ 1,000,000.0			$ 1,000,000.0		$ 1,600,000	$ 2,900,000
Investment in the period					0		400,000	2,000,000.0
Equity method investment, aggregate cost							7,600,000	6,200,000	$ 3,900,000
Other investments, at fair value		204,700,000			204,700,000		209,300,000	221,300,000
Investment in Multiline reinsurer					0		0	0
Investment funded		$ 0			$ 0		0	0
Available-for-sale investment, allowance for credit loss, increase (decrease)							$ (3,600,000)	$ 200,000
Number of Securities \| security		781			781		950	1,166		781	950
Available-for-sale securities, unrealized loss position							$ 221,800,000	$ 339,000,000.0
External Credit Rating, Non Investment Grade
Gain (Loss) on Securities [Line Items]
Available-for-sale securities, unrealized loss position		$ 400,000			$ 400,000		1,200,000
Investment, Identifier [Axis]: Unfunded Commitment, Apollo Real Estate Fund
Gain (Loss) on Securities [Line Items]
Unfunded commitment		4,100,000			4,100,000		4,100,000
Investment, Identifier [Axis]: Unfunded Commitment, Energy fund
Gain (Loss) on Securities [Line Items]
Unfunded commitment		55,000,000.0			55,000,000.0		55,000,000.0
Investment, Identifier [Axis]: Unfunded Commitment, Infrastructure fund
Gain (Loss) on Securities [Line Items]
Unfunded commitment		1,900,000			1,900,000		4,000,000.0
Investment, Identifier [Axis]: Unfunded Commitment, Managed Debt Fund
Gain (Loss) on Securities [Line Items]
Unfunded commitment \| £										£ 6,900,000	£ 6,900,000
Investment, Identifier [Axis]: Unfunded Commitment, Managed lending fund
Gain (Loss) on Securities [Line Items]
Unfunded commitment		700,000			700,000		1,100,000
Investment, Identifier [Axis]: Unfunded Commitment, Real Estate Fund (Sept 2021)
Gain (Loss) on Securities [Line Items]
Unfunded commitment		900,000			900,000		2,200,000
Fair Value, Recurring [Member]
Gain (Loss) on Securities [Line Items]
Investments, fair value		115,000,000.0			115,000,000.0		117,100,000	134,600,000
Fair Value, Recurring [Member] \| Apollo Real Estate Fund
Gain (Loss) on Securities [Line Items]
Other investments, at fair value		20,100,000			20,100,000		23,900,000	25,300,000
Real estate fund \| Fair Value, Recurring [Member]
Gain (Loss) on Securities [Line Items]
Investments, fair value							209,300,000	221,300,000
Commercial mortgage loans
Gain (Loss) on Securities [Line Items]
Fair market value, trading		133,700,000			133,700,000		274,900,000	312,100,000
Middle market loans
Gain (Loss) on Securities [Line Items]
Fair market value, trading		64,000,000.0			64,000,000.0		84,800,000	106,900,000
Privately-held investments
Gain (Loss) on Securities [Line Items]
Fair market value, trading							475,000,000.0	533,000,000.0
Real estate fund (Sept 2021) \| Fair Value, Recurring [Member]
Gain (Loss) on Securities [Line Items]
Investments, fair value		37,400,000			37,400,000		39,800,000	40,600,000
Infrastructure fund \| Fair Value, Recurring [Member]
Gain (Loss) on Securities [Line Items]
Investments, fair value		11,700,000			11,700,000		10,800,000	8,200,000
Managed Lending Fund (Dec 2020) \| Fair Value, Recurring [Member]
Gain (Loss) on Securities [Line Items]
Investments, fair value		18,400,000			18,400,000		15,900,000	12,700,000
Pledge Accounts, Custodian Bank (April 2021) \| Fair Value, Recurring [Member]
Gain (Loss) on Securities [Line Items]
Investments, fair value		2,000,000			2,000,000		1,700,000	1,300,000
Managed debt fund \| Fair Value, Recurring [Member]
Gain (Loss) on Securities [Line Items]
Investments, fair value		100,000			100,000		100,000	0
MVI
Gain (Loss) on Securities [Line Items]
Investment in the period	$ 800,000				0	$ 400,000	0	400,000
Equity method investment, aggregate cost		1,100,000			1,100,000		1,000,000.0	800,000	500,000
Gross realized and unrealized gains (loss)							200,000	0	100,000
Investment in Multiline reinsurer					0		0	0
Digital Re
Gain (Loss) on Securities [Line Items]
Investment in the period					0		0	0
Equity method investment, ownership percentage																				49.00%
Equity method investment, aggregate cost		200,000			200,000		200,000	200,000	200,000											$ 2,300,000
Investment in Multiline reinsurer					0		0	0
Multi-Line Insurer
Gain (Loss) on Securities [Line Items]
Investment in the period				$ 0	0		400,000	1,600,000
Equity method investment, aggregate cost		6,800,000			6,800,000		6,400,000	5,200,000	3,200,000
Other investments, at fair value																		$ 5,000,000.0
Gross realized and unrealized gains (loss)		$ 300,000	$ 400,000		500,000	$ 800,000	800,000	(400,000)	$ 200,000
Investment in Multiline reinsurer					$ 0		$ 0	$ 0
Limited Partner
Gain (Loss) on Securities [Line Items]
Restricted assets														$ 10,000,000	$ 20,000,000.0				$ 100,000,000.0
Limited Partner \| Real estate fund \| Apollo Real Estate Fund
Gain (Loss) on Securities [Line Items]
Restricted assets														$ 30,000,000.0
Limited Partner \| Infrastructure fund
Gain (Loss) on Securities [Line Items]
Restricted assets													$ 15,000,000.0
Limited Partner \| Managed lending fund
Gain (Loss) on Securities [Line Items]
Restricted assets																$ 2,800,000	$ 10,500,000
Limited Partner \| Managed debt fund
Gain (Loss) on Securities [Line Items]
Restricted assets \| £												£ 7,000,000.0