Benefits and Pension Plans - Asset Categories (Details)	12 Months Ended
Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2017
Qualified Plan
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	100.00%	100.00%	100.00%
Percentage of Plan Assets	100.00%	100.00%	100.00%
Expected long term return on plan assets (as a percent)	5.60%	5.40%	6.50%
NEPTCO \| Qualified Plan
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	100.00%	100.00%	100.00%
Percentage of Plan Assets	100.00%	100.00%	100.00%
Expected long term return on plan assets (as a percent)	5.40%	5.20%	6.50%
Equity Securities \| Maximum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	80.00%	80.00%	80.00%
Equity Securities \| Qualified Plan
Target allocation and weighted-average asset allocations
Percentage of Plan Assets	44.00%	46.00%	39.00%
Equity Securities \| Qualified Plan \| Minimum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	10.00%	10.00%	10.00%
Equity Securities \| NEPTCO \| Maximum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	80.00%	80.00%	80.00%
Equity Securities \| NEPTCO \| Qualified Plan
Target allocation and weighted-average asset allocations
Percentage of Plan Assets	44.00%	46.00%	43.00%
Equity Securities \| NEPTCO \| Qualified Plan \| Minimum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	10.00%	10.00%	10.00%
Debt Securities \| Maximum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	70.00%	70.00%	70.00%
Debt Securities \| Qualified Plan
Target allocation and weighted-average asset allocations
Percentage of Plan Assets	56.00%	54.00%	61.00%
Debt Securities \| Qualified Plan \| Minimum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	20.00%	20.00%	20.00%
Debt Securities \| NEPTCO \| Maximum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	70.00%	70.00%	70.00%
Debt Securities \| NEPTCO \| Qualified Plan
Target allocation and weighted-average asset allocations
Percentage of Plan Assets	56.00%	54.00%	51.00%
Debt Securities \| NEPTCO \| Qualified Plan \| Minimum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	20.00%	20.00%	20.00%
Other \| Maximum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	100.00%	100.00%	100.00%
Other \| Qualified Plan \| Minimum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	0.00%	0.00%	0.00%
Other \| NEPTCO \| Maximum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	100.00%	100.00%	100.00%
Other \| NEPTCO \| Qualified Plan
Target allocation and weighted-average asset allocations
Percentage of Plan Assets			6.00%
Other \| NEPTCO \| Qualified Plan \| Minimum
Target allocation and weighted-average asset allocations
Total target allocation (as a percent)	0.00%	0.00%	0.00%

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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- References

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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