Derivative Financial Instruments - Narrative (Details) $ in Millions	6 Months Ended
Jun. 30, 2026 USD ($) counterparty contract	Dec. 31, 2025 USD ($) contract
Derivative
Fair value hedging adjustments for hedged assets	$ 0
Fair value hedging adjustments for hedged liabilities		$ 0
Number of counterparties, net exposure threshold set to zero \| counterparty	1
All Counterparties Except One
Derivative
Counterparties, collateral required threshold	0.00%
Call options and interest rate swaps \| Location, Statement of Financial Position, Balance [Axis]: fnf:DerivativesForTradingAndInvestment \| Derivatives not designated as hedging instruments
Derivative
Collateral posted	$ 1,267	1,185
Equity options \| Location, Statement of Financial Position, Balance [Axis]: us-gaap:CashAndCashEquivalentsAtCarryingValue \| Derivatives not designated as hedging instruments
Derivative
Collateral posted	851	928
Equity options \| Location, Statement of Financial Position, Balance [Axis]: fnf:DerivativesForTradingAndInvestment \| Derivatives not designated as hedging instruments
Derivative
Net credit risk	$ 46	$ 34
Futures contracts
Derivative
Number of instruments held \| contract	240	172
Collateral held	$ 5	$ 4

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Number of Counterparties, Net Exposure Threshold Not Set to Zero

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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Fair value, after effect of master netting arrangement and deduction of obligation to return financial collateral not offset and financial instrument subject to master netting arrangement not offset, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and contract can be net settled by means outside contract or delivery of asset. Includes derivative not subject to master netting arrangement or similar agreement.

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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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The number of derivative instruments of a particular group held by the entity.

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Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk, remaining after discontinued hedge. Excludes cumulative basis adjustment related to foreign exchange risk.

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Amount of cumulative increase (decrease) in fair value of hedged liability in fair value hedge, attributable to hedged risk, remaining after discontinued hedge. Excludes cumulative basis adjustment related to foreign exchange risk.

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