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Schedule - Expense Example {Transposed} {- Western Asset Institutional Government Reserves Investor Shares} link:presentationLink link:calculationLink link:definitionLink 000105 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Government Reserves Investor Shares} link:presentationLink link:calculationLink link:definitionLink 000106 - Schedule - Annual Total Returns - Western Asset Institutional Government Reserves Investor Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000107 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Government Reserves Investor Shares} link:presentationLink link:calculationLink link:definitionLink 000108 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Government Reserves Investor Shares link:presentationLink link:calculationLink link:definitionLink 000109 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Government Reserves) (Investor) link:presentationLink link:calculationLink link:definitionLink 000111 - 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Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Tax Free Reserves Investor Shares} link:presentationLink link:calculationLink link:definitionLink 000118 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Tax Free Reserves Investor Shares link:presentationLink link:calculationLink link:definitionLink 000119 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Tax Free Reserves) (Investor) link:presentationLink link:calculationLink link:definitionLink 000121 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional AMT Free Municipal Money Market Fund) (Investor) link:presentationLink link:calculationLink link:definitionLink 000122 - Schedule - Shareholder Fees {- Western Asset Institutional AMT Free Municipal Money Market Fund Investor Shares} link:presentationLink link:calculationLink link:definitionLink 000123 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional AMT Free Municipal Money Market Fund Investor Shares} link:presentationLink link:calculationLink link:definitionLink 000124 - Schedule - Expense Example {Transposed} {- Western Asset Institutional AMT Free Municipal Money Market Fund Investor Shares} link:presentationLink link:calculationLink link:definitionLink 000125 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional AMT Free Municipal Money Market Fund Investor Shares} link:presentationLink link:calculationLink link:definitionLink 000126 - Schedule - Annual Total Returns - Western Asset Institutional AMT Free Municipal Money Market Fund Investor Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000127 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional AMT Free Municipal Money Market Fund Investor Shares} link:presentationLink link:calculationLink link:definitionLink 000128 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional AMT Free Municipal Money Market Fund Investor Shares link:presentationLink link:calculationLink link:definitionLink 000129 - 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Schedule - Annual Total Returns - Western Asset Institutional Liquid Reserves Administrative Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000137 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Liquid Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000138 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Liquid Reserves Administrative Shares link:presentationLink link:calculationLink link:definitionLink 000139 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Liquid Reserves) (Administrative) link:presentationLink link:calculationLink link:definitionLink 000141 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional Cash Reserves) (Administrative) link:presentationLink link:calculationLink link:definitionLink 000142 - Schedule - Shareholder Fees {- Western Asset Institutional Cash Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000143 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional Cash Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000144 - Schedule - Expense Example {Transposed} {- Western Asset Institutional Cash Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000145 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Cash Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000146 - Schedule - Annual Total Returns - Western Asset Institutional Cash Reserves Administrative Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000147 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Cash Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000148 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Cash Reserves Administrative Shares link:presentationLink link:calculationLink link:definitionLink 000149 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Cash Reserves) (Administrative) link:presentationLink link:calculationLink link:definitionLink 000151 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional U.S. Treasury Reserves) (Administrative) link:presentationLink link:calculationLink link:definitionLink 000152 - Schedule - Shareholder Fees {- Western Asset Institutional U.S. Treasury Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000153 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional U.S. Treasury Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000154 - Schedule - Expense Example {Transposed} {- Western Asset Institutional U.S. Treasury Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000155 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional U.S. Treasury Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000156 - Schedule - Annual Total Returns - Western Asset Institutional U.S. Treasury Reserves Administrative Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000157 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional U.S. Treasury Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000158 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional U.S. Treasury Reserves Administrative Shares link:presentationLink link:calculationLink link:definitionLink 000159 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional U.S. Treasury Reserves) (Administrative) link:presentationLink link:calculationLink link:definitionLink 000161 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional Government Reserves) (Administrative) link:presentationLink link:calculationLink link:definitionLink 000162 - Schedule - Shareholder Fees {- Western Asset Institutional Government Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000163 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional Government Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000164 - Schedule - Expense Example {Transposed} {- Western Asset Institutional Government Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000165 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Government Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000166 - Schedule - Annual Total Returns - Western Asset Institutional Government Reserves Administrative Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000167 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Government Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000168 - Document - Risk/Return Detail {Unlabeled} - 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Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Tax Free Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000176 - Schedule - Annual Total Returns - Western Asset Institutional Tax Free Reserves Administrative Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000177 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Tax Free Reserves Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000178 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Tax Free Reserves Administrative Shares link:presentationLink link:calculationLink link:definitionLink 000179 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Tax Free Reserves) (Administrative) link:presentationLink link:calculationLink link:definitionLink 000181 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional AMT Free Municipal Money Market Fund) (Administrative) link:presentationLink link:calculationLink link:definitionLink 000182 - Schedule - Shareholder Fees {- Western Asset Institutional AMT Free Municipal Money Market Fund Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000183 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional AMT Free Municipal Money Market Fund Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000184 - Schedule - Expense Example {Transposed} {- Western Asset Institutional AMT Free Municipal Money Market Fund Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000185 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional AMT Free Municipal Money Market Fund Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000186 - Schedule - Annual Total Returns - Western Asset Institutional AMT Free Municipal Money Market Fund Administrative Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000187 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional AMT Free Municipal Money Market Fund Administrative Shares} link:presentationLink link:calculationLink link:definitionLink 000188 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional AMT Free Municipal Money Market Fund Administrative Shares link:presentationLink link:calculationLink link:definitionLink 000189 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional AMT Free Municipal Money Market Fund) (Administrative) link:presentationLink link:calculationLink link:definitionLink 000191 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional Cash Reserves) (L Shares) link:presentationLink link:calculationLink link:definitionLink 000192 - Schedule - Shareholder Fees {- Western Asset Institutional Cash Reserves Class L} link:presentationLink link:calculationLink link:definitionLink 000193 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional Cash Reserves Class L} link:presentationLink link:calculationLink link:definitionLink 000194 - Schedule - Expense Example {Transposed} {- Western Asset Institutional Cash Reserves Class L} link:presentationLink link:calculationLink link:definitionLink 000195 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Cash Reserves Class L} link:presentationLink link:calculationLink link:definitionLink 000196 - Schedule - Annual Total Returns - Western Asset Institutional Cash Reserves Class L [BarChart] link:presentationLink link:calculationLink link:definitionLink 000197 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Cash Reserves Class L} link:presentationLink link:calculationLink link:definitionLink 000198 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Cash Reserves Class L link:presentationLink link:calculationLink link:definitionLink 000199 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Cash Reserves) (L shares) link:presentationLink link:calculationLink link:definitionLink 000201 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional Cash Reserves) (Premium) link:presentationLink link:calculationLink link:definitionLink 000202 - Schedule - Shareholder Fees {- Western Asset Institutional Cash Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000203 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional Cash Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000204 - Schedule - Expense Example {Transposed} {- Western Asset Institutional Cash Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000205 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Cash Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000206 - Schedule - Annual Total Returns - Western Asset Institutional Cash Reserves Premium Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000207 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Cash Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000208 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Cash Reserves Premium Shares link:presentationLink link:calculationLink link:definitionLink 000209 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Cash Reserves) (Premium) link:presentationLink link:calculationLink link:definitionLink 000211 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional Cash Reserves) (S Shares) link:presentationLink link:calculationLink link:definitionLink 000212 - Schedule - Shareholder Fees {- Western Asset Institutional Cash Reserves Class S} link:presentationLink link:calculationLink link:definitionLink 000213 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional Cash Reserves Class S} link:presentationLink link:calculationLink link:definitionLink 000214 - Schedule - Expense Example {Transposed} {- Western Asset Institutional Cash Reserves Class S} link:presentationLink link:calculationLink link:definitionLink 000215 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Cash Reserves Class S} link:presentationLink link:calculationLink link:definitionLink 000216 - Schedule - Annual Total Returns - Western Asset Institutional Cash Reserves Class S [BarChart] link:presentationLink link:calculationLink link:definitionLink 000217 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Cash Reserves Class S} link:presentationLink link:calculationLink link:definitionLink 000218 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Cash Reserves Class S link:presentationLink link:calculationLink link:definitionLink 000219 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Cash Reserves) (S Shares) link:presentationLink link:calculationLink link:definitionLink 000221 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional Government Reserves) (Premium) link:presentationLink link:calculationLink link:definitionLink 000222 - Schedule - Shareholder Fees {- Western Asset Institutional Government Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000223 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional Government Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000224 - Schedule - Expense Example {Transposed} {- Western Asset Institutional Government Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000225 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Government Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000226 - Schedule - Annual Total Returns - Western Asset Institutional Government Reserves Premium Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000227 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Government Reserves Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000228 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Government Reserves Premium Shares link:presentationLink link:calculationLink link:definitionLink 000229 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Government Reserves) (Premium) link:presentationLink link:calculationLink link:definitionLink 000231 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional AMT Free Municipal Money Market Fund) (Premium) link:presentationLink link:calculationLink link:definitionLink 000232 - Schedule - Shareholder Fees {- Western Asset Institutional AMT Free Municipal Money Market Fund Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000233 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional AMT Free Municipal Money Market Fund Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000234 - Schedule - Expense Example {Transposed} {- Western Asset Institutional AMT Free Municipal Money Market Fund Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000235 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional AMT Free Municipal Money Market Fund Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000236 - Schedule - Annual Total Returns - Western Asset Institutional AMT Free Municipal Money Market Fund Premium Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000237 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional AMT Free Municipal Money Market Fund Premium Shares} link:presentationLink link:calculationLink link:definitionLink 000238 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional AMT Free Municipal Money Market Fund Premium Shares link:presentationLink link:calculationLink link:definitionLink 000239 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional AMT Free Municipal Money Market Fund) (Premium) link:presentationLink link:calculationLink link:definitionLink 000241 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional Liquid Reserves) (Liquid Reserves Shares) link:presentationLink link:calculationLink link:definitionLink 000242 - Schedule - Shareholder Fees {- Western Asset Institutional Liquid Reserves SVB Securities Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000243 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional Liquid Reserves SVB Securities Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000244 - Schedule - Expense Example {Transposed} {- Western Asset Institutional Liquid Reserves SVB Securities Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000245 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Liquid Reserves SVB Securities Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000246 - Schedule - Annual Total Returns - Western Asset Institutional Liquid Reserves SVB Securities Liquid Reserves Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000247 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Liquid Reserves SVB Securities Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000248 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Liquid Reserves SVB Securities Liquid Reserves Shares link:presentationLink link:calculationLink link:definitionLink 000249 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Liquid Reserves) (Liquid Reserves Shares) link:presentationLink link:calculationLink link:definitionLink 000251 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional Liquid Reserves) (Institutional Liquid Reserves Shares) link:presentationLink link:calculationLink link:definitionLink 000252 - Schedule - Shareholder Fees {- Western Asset Institutional Liquid Reserves SVB Securities Institutional Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000253 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional Liquid Reserves SVB Securities Institutional Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000254 - Schedule - Expense Example {Transposed} {- Western Asset Institutional Liquid Reserves SVB Securities Institutional Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000255 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Liquid Reserves SVB Securities Institutional Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000256 - Schedule - Annual Total Returns - Western Asset Institutional Liquid Reserves SVB Securities Institutional Liquid Reserves Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000257 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Liquid Reserves SVB Securities Institutional Liquid Reserves Shares} link:presentationLink link:calculationLink link:definitionLink 000258 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Liquid Reserves SVB Securities Institutional Liquid Reserves Shares link:presentationLink link:calculationLink link:definitionLink 000259 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Liquid Reserves) (Institutional Liquid Reserves Shares) link:presentationLink link:calculationLink link:definitionLink 000261 - Document - Risk/Return Summary {Unlabeled} - (Western Asset Institutional Cash Reserves) (Horizon Shares) link:presentationLink link:calculationLink link:definitionLink 000262 - Schedule - Shareholder Fees {- Western Asset Institutional Cash Reserves SVB Securities Horizon Shares} link:presentationLink link:calculationLink link:definitionLink 000263 - Schedule - Annual Fund Operating Expenses {- Western Asset Institutional Cash Reserves SVB Securities Horizon Shares} link:presentationLink link:calculationLink link:definitionLink 000264 - Schedule - Expense Example {Transposed} {- Western Asset Institutional Cash Reserves SVB Securities Horizon Shares} link:presentationLink link:calculationLink link:definitionLink 000265 - Schedule - Expense Example, No Redemption {Transposed} {- Western Asset Institutional Cash Reserves SVB Securities Horizon Shares} link:presentationLink link:calculationLink link:definitionLink 000266 - Schedule - Annual Total Returns - Western Asset Institutional Cash Reserves SVB Securities Horizon Shares [BarChart] link:presentationLink link:calculationLink link:definitionLink 000267 - Schedule - Average Annual Total Returns {Transposed} {- Western Asset Institutional Cash Reserves SVB Securities Horizon Shares} link:presentationLink link:calculationLink link:definitionLink 000268 - Document - Risk/Return Detail {Unlabeled} - Western Asset Institutional Cash Reserves SVB Securities Horizon Shares link:presentationLink link:calculationLink link:definitionLink 000269 - Disclosure - Risk/Return Detail Data {Elements} - (Western Asset Institutional Cash Reserves) (Horizon Shares) link:presentationLink link:calculationLink link:definitionLink