Contractholder Funds - Narrative (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2026	Dec. 31, 2025
Insurance [Abstract]
Decrease in total benefits and other changes in policy reserves	$ 268	$ 22

Policyholder Benefits And Claims Incurred, Net, Life and Annuity, Change In Policy Reserves, Increase (Decrease)

No definition available.

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Namespace Prefix:	fg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration