v3.26.1
Shareholder Report
 6 Months Ended
Mar. 31, 2026
USD ($)
$ / shares
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Legg Mason Global Asset Management Trust
Entity Central Index Key 0001474103
Entity Investment Company Type N-1A
Document Period End Date Mar. 31, 2026
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Class A  
Shareholder Report [Line Items]  
Fund Name BrandywineGLOBAL - Diversified US Large Cap Value Fund
Class Name Class A
Trading Symbol LBWAX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BrandywineGLOBAL - Diversified US Large Cap Value Fund for the period October 1, 2025, to March 31, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at 877-6LM-FUND/656-3863.
Additional Information Phone Number 877-6LM-FUND/656-3863
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment*,†
Class A
$57
1.10%
[1],[2]
Expenses Paid, Amount $ 57
Expense Ratio, Percent 1.10%
Net Assets $ 102,212,888
Holdings Count | $ / shares 222
Investment Company Portfolio Turnover 44.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of March 31, 2026)
Total Net Assets
$102,212,888
Total Number of Portfolio Holdings
222
Portfolio Turnover Rate
44%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of March 31, 2026)
Portfolio Composition* (% of Total Investments)
image
 [3]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class C  
Shareholder Report [Line Items]  
Fund Name BrandywineGLOBAL - Diversified US Large Cap Value Fund
Class Name Class C
Trading Symbol LBWCX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BrandywineGLOBAL - Diversified US Large Cap Value Fund for the period October 1, 2025, to March 31, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at 877-6LM-FUND/656-3863.
Additional Information Phone Number 877-6LM-FUND/656-3863
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment*,†
Class C
$93
1.81%
[4],[5]
Expenses Paid, Amount $ 93
Expense Ratio, Percent 1.81%
Net Assets $ 102,212,888
Holdings Count | $ / shares 222
Investment Company Portfolio Turnover 44.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of March 31, 2026)
Total Net Assets
$102,212,888
Total Number of Portfolio Holdings
222
Portfolio Turnover Rate
44%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of March 31, 2026)
Portfolio Composition* (% of Total Investments)
image
 [6]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class R  
Shareholder Report [Line Items]  
Fund Name BrandywineGLOBAL - Diversified US Large Cap Value Fund
Class Name Class R
Trading Symbol LBDRX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BrandywineGLOBAL - Diversified US Large Cap Value Fund for the period October 1, 2025, to March 31, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at 877-6LM-FUND/656-3863.
Additional Information Phone Number 877-6LM-FUND/656-3863
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment*,†
Class R
$70
1.35%
[7],[8]
Expenses Paid, Amount $ 70
Expense Ratio, Percent 1.35%
Net Assets $ 102,212,888
Holdings Count | $ / shares 222
Investment Company Portfolio Turnover 44.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of March 31, 2026)
Total Net Assets
$102,212,888
Total Number of Portfolio Holdings
222
Portfolio Turnover Rate
44%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of March 31, 2026)
Portfolio Composition* (% of Total Investments)
image
 [9]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class I  
Shareholder Report [Line Items]  
Fund Name BrandywineGLOBAL - Diversified US Large Cap Value Fund
Class Name Class I
Trading Symbol LBWIX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BrandywineGLOBAL - Diversified US Large Cap Value Fund for the period October 1, 2025, to March 31, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at 877-6LM-FUND/656-3863.
Additional Information Phone Number 877-6LM-FUND/656-3863
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment*,†
Class I
$41
0.80%
[10],[11]
Expenses Paid, Amount $ 41
Expense Ratio, Percent 0.80%
Net Assets $ 102,212,888
Holdings Count | $ / shares 222
Investment Company Portfolio Turnover 44.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of March 31, 2026)
Total Net Assets
$102,212,888
Total Number of Portfolio Holdings
222
Portfolio Turnover Rate
44%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of March 31, 2026)
Portfolio Composition* (% of Total Investments)
image
 [12]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
Class IS  
Shareholder Report [Line Items]  
Fund Name BrandywineGLOBAL - Diversified US Large Cap Value Fund
Class Name Class IS
Trading Symbol LBISX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about BrandywineGLOBAL - Diversified US Large Cap Value Fund for the period October 1, 2025, to March 31, 2026.
Additional Information [Text Block] You can find additional information about the Fund at https://www.franklintempleton.com/regulatory-fund-documents. You can also request this information by contacting us at 877-6LM-FUND/656-3863.
Additional Information Phone Number 877-6LM-FUND/656-3863
Additional Information Website https://www.franklintempleton.com/regulatory-fund-documents
Expenses [Text Block]
WHAT WERE THE FUND COSTS FOR THE LAST SIX MONTHS? (based on a hypothetical $10,000 investment)
Class Name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment*,†
Class IS
$36
0.70%
[13],[14]
Expenses Paid, Amount $ 36
Expense Ratio, Percent 0.70%
Net Assets $ 102,212,888
Holdings Count | $ / shares 222
Investment Company Portfolio Turnover 44.00%
Additional Fund Statistics [Text Block]
KEY FUND STATISTICS (as of March 31, 2026)
Total Net Assets
$102,212,888
Total Number of Portfolio Holdings
222
Portfolio Turnover Rate
44%
Holdings [Text Block]
WHAT DID THE FUND INVEST IN? (as of March 31, 2026)
Portfolio Composition* (% of Total Investments)
image
 [15]
Updated Prospectus Web Address https://www.franklintempleton.com/regulatory-fund-documents
[1]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[2]
† Annualized.
[3]
* Does not include derivatives, except purchased options, if any.  
[4]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[5]
† Annualized.
[6]
* Does not include derivatives, except purchased options, if any.  
[7]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[8]
† Annualized.
[9]
* Does not include derivatives, except purchased options, if any.  
[10]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[11]
† Annualized.
[12]
* Does not include derivatives, except purchased options, if any.  
[13]
* Reflects fee waivers and/or expense reimbursements, without which expenses would have been higher.
[14]
† Annualized.
[15]
* Does not include derivatives, except purchased options, if any.