The fund invests in a portfolio of fixed income securities of various maturities and, under normal market conditions, will invest at least 80% of its net assets, including the amount of borrowing for investment purposes, if any, in debt and fixed income securities. Although the fund may invest in securities of any maturity, the fund normally expects to maintain a dollar-weighted average effective duration within 30% of the average duration of the domestic bond market as a whole as estimated by the fund’s subadvisers. Effective duration seeks to measure the expected sensitivity of market price to changes in interest rates, taking into account the anticipated effects of structural complexities (for example, some bonds can be prepaid by the issuer).

The fund may invest up to 20% of its total assets in non-U.S. dollar denominated securities. Up to 20% of the fund’s net assets may be invested in debt securities that are not rated in the Baa or BBB categories or above at the time of purchase by one or more Nationally Recognized Statistical Rating Organizations (“NRSROs”) or, if unrated, securities of comparable quality at the time of purchase (as determined by the subadvisers). Securities rated in the Baa or BBB categories or above by one or more NRSROs or unrated securities of comparable quality are known as “investment grade securities.” Securities rated below investment grade are commonly known as “junk bonds” or “high yield securities.” The fund may invest up to 25% of its total assets in the securities of non-U.S. issuers. The fund may invest a substantial portion of its assets in mortgage-backed and asset-backed securities.

The fund may also enter into various exchange-traded and over-the-counter derivative transactions for both hedging and non-hedging purposes, including for purposes of enhancing returns. These derivative transactions include, but are not limited to, futures, options, swaps, foreign currency futures and forwards.

In particular, the fund may use interest rate swaps, credit default swaps (including buying and selling credit default swaps on individual securities and/or baskets of securities), options (including options on credit default swaps and options on futures) and futures contracts to a significant extent, although the amounts invested in these instruments may change from time to time. Other instruments may also be used to a significant extent from time to time.

S000000714 [Member] Investment Strategy - Western Asset Core Plus Bond Fund	Dec. 31, 2025
Prospectus [Line Items]
Strategy [Heading]	Principal investment strategies
Strategy Narrative [Text Block]	The fund invests in a portfolio of fixed income securities of various maturities and, under normal market conditions, will invest at least 80% of its net assets, including the amount of borrowing for investment purposes, if any, in debt and fixed income securities. Although the fund may invest in securities of any maturity, the fund normally expects to maintain a dollar-weighted average effective duration within 30% of the average duration of the domestic bond market as a whole as estimated by the fund’s subadvisers. Effective duration seeks to measure the expected sensitivity of market price to changes in interest rates, taking into account the anticipated effects of structural complexities (for example, some bonds can be prepaid by the issuer). The fund may invest up to 20% of its total assets in non-U.S. dollar denominated securities. Up to 20% of the fund’s net assets may be invested in debt securities that are not rated in the Baa or BBB categories or above at the time of purchase by one or more Nationally Recognized Statistical Rating Organizations (“NRSROs”) or, if unrated, securities of comparable quality at the time of purchase (as determined by the subadvisers). Securities rated in the Baa or BBB categories or above by one or more NRSROs or unrated securities of comparable quality are known as “investment grade securities.” Securities rated below investment grade are commonly known as “junk bonds” or “high yield securities.” The fund may invest up to 25% of its total assets in the securities of non-U.S. issuers. The fund may invest a substantial portion of its assets in mortgage-backed and asset-backed securities. The fund may also enter into various exchange-traded and over-the-counter derivative transactions for both hedging and non-hedging purposes, including for purposes of enhancing returns. These derivative transactions include, but are not limited to, futures, options, swaps, foreign currency futures and forwards. In particular, the fund may use interest rate swaps, credit default swaps (including buying and selling credit default swaps on individual securities and/or baskets of securities), options (including options on credit default swaps and options on futures) and futures contracts to a significant extent, although the amounts invested in these instruments may change from time to time. Other instruments may also be used to a significant extent from time to time.