Segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2015
Segment Reporting Information [Line Items]
Net Sales	$ 1,271.1	$ 1,052.7	$ 2,519.9	$ 2,126.6
Interest expense (income), net	77.2	59.8	155.0	119.9
Other expense	90.9	28.8	106.8	83.4
(Loss) earnings before income taxes	(5.6)	(38.9)	33.6	(112.7)
Depreciation and amortization	76.4	63.2	151.2	126.3
Assets	9,204.5		9,204.5		$ 9,220.4
Post Consumer Brands Segment [Member]
Segment Reporting Information [Line Items]
Net Sales	440.1	243.9	851.7	461.4
Segment Profit	74.7	50.8	137.6	88.4
Depreciation and amortization	26.2	12.0	52.5	24.2
Assets	3,433.6		3,433.6		3,473.0
Michael Foods Group Segment [Member]
Segment Reporting Information [Line Items]
Net Sales	557.7	550.3	1,144.1	1,149.6
Segment Profit	89.6	39.8	170.4	81.9
Depreciation and amortization	36.1	36.5	70.5	73.1
Assets	3,535.4		3,535.4		3,506.0
Active Nutrition segment [Member] [Member]
Segment Reporting Information [Line Items]
Net Sales	143.8	134.6	259.6	265.0
Segment Profit	13.8	(4.5)	24.3	(10.8)
Depreciation and amortization	6.2	6.9	12.4	13.8
Assets	641.8		641.8		645.4
Private Brands segment [Member]
Segment Reporting Information [Line Items]
Net Sales	129.7	124.9	265.3	252.7
Segment Profit	7.7	10.4	20.6	17.3
Depreciation and amortization	6.2	6.5	12.4	12.5
Assets	653.3		653.3		651.6
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Other Expenses	23.3	46.8	57.5	86.2
Depreciation and amortization	1.7	1.3	3.4	2.7
Assets	940.4		940.4		$ 944.4
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net Sales	(0.2)	(1.0)	(0.8)	(2.1)
Total Segment [Member]
Segment Reporting Information [Line Items]
Segment Profit	185.8	96.5	352.9	176.8
Depreciation and amortization	$ 74.7	$ 61.9	$ 147.8	$ 123.6