Investments - Aggregate Contractual or Notional Amounts and Estimated Fair Values Related to Derivative Financial Instruments (Details) - Without Hedge Designation - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Options – purchased \| Options – purchased
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/Notional Amount	$ 95	$ 268
Estimated Fair Value, Asset	1	2
Estimated Fair Value, Liability
Futures – short \| Futures – short
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/Notional Amount	1	167
Estimated Fair Value, Asset		1
Estimated Fair Value, Liability
Warrants
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/Notional Amount	1	1
Estimated Fair Value, Asset	1	1
Estimated Fair Value, Liability
Interest rate swaps
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/Notional Amount	474	300
Estimated Fair Value, Asset		4
Estimated Fair Value, Liability
Credit default swap index - purchased
Gross Estimated Fair Values of Derivative Positions [Abstract]
Contractual/Notional Amount		2,000
Estimated Fair Value, Asset
Estimated Fair Value, Liability

LOEWS CORP 10-Q