v3.20.4

Subsequent Events (Details) - USD ($) $ in Millions	Feb. 01, 2021	Jan. 25, 2021	Dec. 31, 2020	Dec. 31, 2019
8th Avenue
Subsequent Event [Line Items]
Equity Method Investment, Ownership Percentage			60.50%	60.50%
Peter Pan | Subsequent Event
Subsequent Event [Line Items]
Payments to Acquire Businesses, Base Purchase Price		$ 102.0
Payment at closing		$ 103.4
Almark Foods | Subsequent Event
Subsequent Event [Line Items]
Payments to Acquire Businesses, Base Purchase Price	$ 52.0
Payment at closing	$ 51.3

X

- Definition

Payments to Acquire Businesses, Base Purchase Price

+ References

No definition available.

+ Details

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Namespace Prefix:	post_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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Balance Type:	na
Period Type:	instant

X

- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

+ Details

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Balance Type:	credit
Period Type:	duration

X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
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- Details

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X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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Balance Type:
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X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: