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Business Segments - (Summary Of Company's Segment Results) (Parenthetical) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Operating Segments [Member] | U S Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Net investment income	$ 67	$ 93	$ 81
Operating Segments [Member] | Corporate Operations [Member]
Segment Reporting Information [Line Items]
Net investment income	30	25	22
Operating Segments [Member] | International And Structured Finance Insurance [Member]
Segment Reporting Information [Line Items]
Net investment income	11	23	17
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net investment income	$ (24)	$ (25)	$ (25)

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- Definition

Amount after accretion (amortization) of discount (premium), and investment expense, of interest income and dividend income on nonoperating securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(8))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Section S99
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