Business Segments (Summary Of Company's Segment Results) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Operating Segments [Member] \| U S Public Finance Insurance [Member]
Segment Reporting [Line Items]
Net investment income	$ 15	$ 14	$ 45	$ 44
Operating Segments [Member] \| Corporate Operations [Member]
Segment Reporting [Line Items]
Net investment income	6	6	17	19
Operating Segments [Member] \| International And Structured Finance Insurance [Member]
Segment Reporting [Line Items]
Net investment income	2	2	8	8
Intersegment Eliminations [Member]
Segment Reporting [Line Items]
Net investment income	$ (6)	$ (5)	$ (18)	$ (17)

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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+ Details