Collateral Financing Agreement With Affiliate (Details) $ in Millions	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($) security
Debt Instrument, Redemption [Line Items]
Margin deposits posted under affiliate financing agreement	$ 450	$ 435
Margin deposits financing with affiliate	$ 450	$ 435
Pre-Capitalized Trust Securities
Debt Instrument, Redemption [Line Items]
Derivative, number of instruments held | security			450,000
Derivative, notional amount			$ 450