S000003998 [Member] Fees and Expenses - Putnam Sustainable Retirement 2040 Fund	Jul. 31, 2025 USD ($)
Prospectus [Line Items]
Expense Heading [Optional Text]	Fees and expenses
Expense Narrative [Text Block]	The following tables describe the fees and expenses you may pay if you buy, hold and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Putnam funds. More information about these and other discounts is available from your financial professional and in How do I buy fund shares? beginning on page 150 of the fund’s prospectus, in the Appendix to the fund’s prospectus, and in How to buy shares beginning on page 50 of the fund’s Statement of Additional Information (“SAI”).
Expense Breakpoint Discounts [Text]	You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Putnam funds.
Expenses Restated to Reflect Current [Text]	Management fees have been restated to reflect the reduced management fee rate that took effect under the fund’s management agreement effective October 1, 2025 based on the number of years remaining until the date referenced in the fund’s name. Consequently, the fund’s total annual fund operating expenses differ from the ratio of expenses to average net assets shown in the fund’s financial highlights.
Expense Breakpoint, Minimum Investment Required [Amount]	$ 50,000
Acquired Fund Fees and Expenses, Based on Estimates [Text]	Estimated amounts for current fiscal year. Actual expenses may differ from estimates.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]	Total annual fund operating expenses do not correlate with the ratios of expenses to average net assets reported in the fund’s financial highlights, which reflect the fund’s operating expenses and do not include acquired fund fees and expenses.
Shareholder Fees Caption [Optional Text]	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Optional Text]	Annual Fund Operating Expenses (expenses you pay each year as a percentage of the value of your investment)
Expense Example [Heading]	Example
Expense Example Narrative [Text Block]	The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. It assumes that you invest $10,000 in the fund for the time periods indicated and then, except as indicated, redeem all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same (except that any applicable fee waiver or expense reimbursement is reflected only through its expiration date). Your actual costs may be higher or lower.
Portfolio Turnover [Heading]	Portfolio turnover
Portfolio Turnover [Text Block]	The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs and may result in higher taxes when the fund’s shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 17%.
Portfolio Turnover, Rate	17.00%

S000003998 [Member] Fees and Expenses - Putnam Sustainable Retirement 2040 Fund

Jul. 31, 2025

USD ($)

Fees and expenses

The following tables describe the fees and expenses you may pay if you buy, hold and sell shares of the fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Putnam funds. More information about these and other discounts is available from your financial professional and in How do I buy fund shares? beginning on page 150 of the fund’s prospectus, in the Appendix to the fund’s prospectus, and in How to buy shares beginning on page 50 of the fund’s Statement of Additional Information (“SAI”).

Expense Breakpoint Discounts [Text]

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $50,000 in Putnam funds.

Expenses Restated to Reflect Current [Text]

Management fees have been restated to reflect the reduced management fee rate that took effect under the fund’s management agreement effective October 1, 2025 based on the number of years remaining until the date referenced in the fund’s name. Consequently, the fund’s total annual fund operating expenses differ from the ratio of expenses to average net assets shown in the fund’s financial highlights.

Expense Breakpoint, Minimum Investment Required [Amount]

$ 50,000

Acquired Fund Fees and Expenses, Based on Estimates [Text]

Estimated amounts for current fiscal year. Actual expenses may differ from estimates.

Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]

Total annual fund operating expenses do not correlate with the ratios of expenses to average net assets reported in the fund’s financial highlights, which reflect the fund’s operating expenses and do not include acquired fund fees and expenses.

Shareholder Fees Caption [Optional Text]

Shareholder Fees (fees paid directly from your investment)

Operating Expenses Caption [Optional Text]

Annual Fund Operating Expenses (expenses you pay each year as a percentage of the value of your investment)

Expense Example [Heading]

Example

Expense Example Narrative [Text Block]

The following hypothetical example is intended to help you compare the cost of investing in the fund with the cost of investing in other funds. It assumes that you invest $10,000 in the fund for the time periods indicated and then, except as indicated, redeem all your shares at the end of those periods. It assumes a 5% return on your investment each year and that the fund’s operating expenses remain the same (except that any applicable fee waiver or expense reimbursement is reflected only through its expiration date). Your actual costs may be higher or lower.

Portfolio Turnover [Heading]

Portfolio turnover

Portfolio Turnover [Text Block]

The fund pays transaction-related costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher turnover rate may indicate higher transaction costs and may result in higher taxes when the fund’s shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or the above example, affect fund performance. The fund’s turnover rate in the most recent fiscal year was 17%.

Portfolio Turnover, Rate

17.00%