Organization	12 Months Ended
Dec. 31, 2019
Accounting Policies [Abstract]
Organization, Consolidation, Basis of Presentation, Business Description and Accounting Policies [Text Block]	(1) Organization – AEI Income & Growth Fund XXI Limited Partnership (“Partnership”) was formed to acquire and lease commercial properties to operating tenants. The Partnership's operations are managed by AEI Fund Management XXI, Inc. (“AFM”), the Managing General Partner. Robert P. Johnson, the Chief Executive Officer and sole director of AFM, serves as the Individual General Partner. AFM is a wholly owned subsidiary of AEI Capital Corporation of which Mr. Johnson and his wife own a majority interest. AEI Fund Management, Inc. (“AEI”), an affiliate of AFM, performs the administrative and operating functions for the Partnership. The terms of the Partnership offering called for a subscription price of $1,000 per Limited Partnership Unit, payable on acceptance of the offer. The Partnership commenced operations on April 14, 1995 when minimum subscriptions of 1,500 Limited Partnership Units ($1,500,000) were accepted. On January 31, 1997, the offering terminated when the maximum subscription limit of 24,000 Limited Partnership Units was reached. Under the terms of the Limited Partnership Agreement, the Limited Partners and General Partners contributed funds of $24,000,000 and $1,000, respectively. During operations, any Net Cash Flow, as defined, which the General Partners determine to distribute will be distributed 90% to the Limited Partners and 10% to the General Partners; provided, however, that such distributions to the General Partners will be subordinated to the Limited Partners first receiving an annual, noncumulative distribution of Net Cash Flow equal to 10% of their Adjusted Capital Contribution, as defined, and, provided further, that in no event will the General Partners receive less than 1% of such Net Cash Flow per annum. Distributions to Limited Partners will be made pro rata by Units. Any Net Proceeds of Sale, as defined, from the sale or financing of properties which the General Partners determine to distribute will, after provisions for debts and reserves, be paid in the following manner: (i) first, 99% to the Limited Partners and 1% to the General Partners until the Limited Partners receive an amount equal to: (a) their Adjusted Capital Contribution plus (b) an amount equal to 10% of their Adjusted Capital Contribution per annum, cumulative but not compounded, to the extent not previously distributed from Net Cash Flow; (ii) any remaining balance will be distributed 90% to the Limited Partners and 10% to the General Partners. Distributions to the Limited Partners will be made pro rata by Units. For tax purposes, profits from operations, other than profits attributable to the sale, exchange, financing, refinancing or other disposition of property, will be allocated first in the same ratio in which, and to the extent, Net Cash Flow is distributed to the Partners for such year. Any additional profits will be allocated in the same ratio as the last dollar of Net Cash Flow is distributed. Net losses from operations will be allocated 99% to the Limited Partners and 1% to the General Partners. For tax purposes, profits arising from the sale, financing, or other disposition of property will be allocated in accordance with the Partnership Agreement as follows: (i) first, to those partners with deficit balances in their capital accounts in an amount equal to the sum of such deficit balances; (ii) second, 99% to the Limited Partners and 1% to the General Partners until the aggregate balance in the Limited Partners' capital accounts equals the sum of the Limited Partners' Adjusted Capital Contributions plus an amount equal to 10% of their Adjusted Capital Contributions per annum, cumulative but not compounded, to the extent not previously allocated; (iii) third, the balance of any remaining gain will then be allocated 90% to the Limited Partners and 10% to the General Partners. Losses will be allocated 98% to the Limited Partners and 2% to the General Partners. The General Partners are not required to currently fund a deficit capital balance. Upon liquidation of the Partnership or withdrawal by a General Partner, the General Partners will contribute to the Partnership an amount equal to the lesser of the deficit balances in their capital accounts or 1% of total Limited Partners' and General Partners' capital contributions. In January 2014, the Managing General Partner mailed a Consent Statement (Proxy) seeking the consent of the Limited Partners to continue the Partnership for an additional 60 months or to initiate the final disposition, liquidation and distribution of all of the Partnership’s properties and assets. On February 14, 2014, the proposal to continue the Partnership was approved with a majority of Units voted in favor of the continuation proposal. As a result, the Managing General Partner will continue the operations of the Partnership. In consideration of the adverse impact COVID-19 is having on the World and U.S. economy, the General Partner believes it is in the best interest of the Partnership to continue operations. The General Partner will re-evaluate the situation in 12 to 24 months and may again submit the option to liquidate to a vote by the Limited Partners at that time.

(1) Organization –

AEI Income & Growth Fund XXI Limited Partnership (“Partnership”) was formed to acquire and lease commercial properties to operating tenants. The Partnership's operations are managed by AEI Fund Management XXI, Inc. (“AFM”), the Managing General Partner. Robert P. Johnson, the Chief Executive Officer and sole director of AFM, serves as the Individual General Partner. AFM is a wholly owned subsidiary of AEI Capital Corporation of which Mr. Johnson and his wife own a majority interest. AEI Fund Management, Inc. (“AEI”), an affiliate of AFM, performs the administrative and operating functions for the Partnership.

The terms of the Partnership offering called for a subscription price of $1,000 per Limited Partnership Unit, payable on acceptance of the offer. The Partnership commenced operations on April 14, 1995 when minimum subscriptions of 1,500 Limited Partnership Units ($1,500,000) were accepted. On January 31, 1997, the offering terminated when the maximum subscription limit of 24,000 Limited Partnership Units was reached. Under the terms of the Limited Partnership Agreement, the Limited Partners and General Partners contributed funds of $24,000,000 and $1,000, respectively.

During operations, any Net Cash Flow, as defined, which the General Partners determine to distribute will be distributed 90% to the Limited Partners and 10% to the General Partners; provided, however, that such distributions to the General Partners will be subordinated to the Limited Partners first receiving an annual, noncumulative distribution of Net Cash Flow equal to 10% of their Adjusted Capital Contribution, as defined, and, provided further, that in no event will the General Partners receive less than 1% of such Net Cash Flow per annum. Distributions to Limited Partners will be made pro rata by Units.

Any Net Proceeds of Sale, as defined, from the sale or financing of properties which the General Partners determine to distribute will, after provisions for debts and reserves, be paid in the following manner: (i) first, 99% to the Limited Partners and 1% to the General Partners until the Limited Partners receive an amount equal to: (a) their Adjusted Capital Contribution plus (b) an amount equal to 10% of their Adjusted Capital Contribution per annum, cumulative but not compounded, to the extent not previously distributed from Net Cash Flow; (ii) any remaining balance will be distributed 90% to the Limited Partners and 10% to the General Partners. Distributions to the Limited Partners will be made pro rata by Units.

For tax purposes, profits from operations, other than profits attributable to the sale, exchange, financing, refinancing or other disposition of property, will be allocated first in the same ratio in which, and to the extent, Net Cash Flow is distributed to the Partners for such year. Any additional profits will be allocated in the same ratio as the last dollar of Net Cash Flow is distributed. Net losses from operations will be allocated 99% to the Limited Partners and 1% to the General Partners.

For tax purposes, profits arising from the sale, financing, or other disposition of property will be allocated in accordance with the Partnership Agreement as follows: (i) first, to those partners with deficit balances in their capital accounts in an amount equal to the sum of such deficit balances; (ii) second, 99% to the Limited Partners and 1% to the General Partners until the aggregate balance in the Limited Partners' capital accounts equals the sum of the Limited Partners' Adjusted Capital Contributions plus an amount equal to 10% of their Adjusted Capital Contributions per annum, cumulative but not compounded, to the extent not previously allocated; (iii) third, the balance of any remaining gain will then be allocated 90% to the Limited Partners and 10% to the General Partners. Losses will be allocated 98% to the Limited Partners and 2% to the General Partners.

The General Partners are not required to currently fund a deficit capital balance. Upon liquidation of the Partnership or withdrawal by a General Partner, the General Partners will contribute to the Partnership an amount equal to the lesser of the deficit balances in their capital accounts or 1% of total Limited Partners' and General Partners' capital contributions.

In January 2014, the Managing General Partner mailed a Consent Statement (Proxy) seeking the consent of the Limited Partners to continue the Partnership for an additional 60 months or to initiate the final disposition, liquidation and distribution of all of the Partnership’s properties and assets. On February 14, 2014, the proposal to continue the Partnership was approved with a majority of Units voted in favor of the continuation proposal. As a result, the Managing General Partner will continue the operations of the Partnership. In consideration of the adverse impact COVID-19 is having on the World and U.S. economy, the General Partner believes it is in the best interest of the Partnership to continue operations. The General Partner will re-evaluate the situation in 12 to 24 months and may again submit the option to liquidate to a vote by the Limited Partners at that time.