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Goodwill and Other Intangibles - Changes in the carrying value of goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2025
Goodwill [Line Items]
Goodwill, beginning balance		$ 305
Goodwill, ending balance		327
Radion Insurance Holdings, LLC
Goodwill [Line Items]
Purchase of Radion	$ 22	$ 22

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Amount, after accumulated impairment loss, of asset representing future economic benefit arising from other asset acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized.

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