Partners' Capital (Details)	3 Months Ended
Mar. 31, 2018 USD ($) $ / shares $ / item shares	Mar. 31, 2017 USD ($) $ / shares $ / item shares
Partners' Capital (Details) [Line Items]
Partners' Capital Account, Distributions	$ 279,801	$ 279,800
Limited Partner [Member]
Partners' Capital (Details) [Line Items]
Partners' Capital Account, Distributions	$ 277,003	$ 277,002
Distributions Per Limited Partnership Unit Outstanding, Basic (in Dollars per share) \| $ / shares	$ 13.84	$ 13.74
Weighted Average Limited Partnership Units Outstanding, Basic (in Shares) \| shares	20,015	20,163
DistributionsPerUnitOfNetIncome (in Dollars per Item) \| $ / item	10.54	9.92
DistributionsPerUnitOfReturnOfCapital (in Dollars per Item) \| $ / item	3.30	3.82
General Partner [Member]
Partners' Capital (Details) [Line Items]
Partners' Capital Account, Distributions	$ 2,798	$ 2,798

No definition available.

Name:	aei20_DistributionsPerUnitOfNetIncome
Namespace Prefix:	aei20_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	aei20_DistributionsPerUnitOfReturnOfCapital
Namespace Prefix:	aei20_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	aei20_PartnersCapitalDetailsLineItems
Namespace Prefix:	aei20_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Cash dividends declared or paid to each outstanding limited partnership unit during the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

+ Details

Name:	us-gaap_DistributionsPerLimitedPartnershipUnitOutstanding
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Total distributions to each class of partners (i.e., general, limited and preferred partners).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

+ Details

Name:	us-gaap_PartnersCapitalAccountDistributions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Weighted average number of limited partnership units outstanding determined by relating the portion of time within a reporting period that limited partnership units have been outstanding to the total time in that period.

+ References

+ Details

Name:	us-gaap_WeightedAverageLimitedPartnershipUnitsOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_LimitedPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_GeneralPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: