Consolidating Financial Information - Schedule of Balance Sheet Information (Detail) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2018	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016
Condensed Balance Sheet [Line Items]
Document Period End Date	Mar. 31, 2018
Interest Payable, Current	$ 62.6	$ 78.0
Other Accrued Liabilities, Current	129.0	125.8
Assets:
Cash and cash equivalents	758.8	270.1	$ 294.6	$ 465.2
Other receivables, net	337.6	266.0
Other Receivables, Net, Current	62.2	19.7
Inventories, net	610.5	496.3
Goodwill (Note 12)	2,280.2	2,277.1
Intangibles, net	1,589.5	1,612.0
Deferred charges and other assets	60.8	43.7
Disposal Group, Including Discontinued Operation, Assets, Noncurrent	0.0	1,376.9
Disposal Group, Including Discontinued Operation, Assets, Current	1,976.0	28,929.2
Assets	8,240.3	35,849.7
Liabilities and Equity:
Short-term Debt	70.3	161.4
Long-term Debt, Excluding Current Maturities	5,248.4	5,543.7
Employee benefit obligations	38.8	38.6
Deferred tax liabilities	285.8	493.2
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent	0.0	156.1
Disposal Group, Including Discontinued Operation, Liabilities, Current	558.6	26,851.3
Stockholders' Equity Attributable to Parent	691.6	758.0
Noncontrolling interests	652.1	1,188.9
Total permanent equity	1,343.7	1,946.9
Total liabilities and equity	8,240.3	35,849.7
Assets, Current	3,805.3	30,036.1
Prepaid Expense and Other Assets	60.2	54.8
Liabilities, Current	1,222.5	27,645.0
Liabilities	6,896.6	33,902.8
Consumer Products Segment [Member]
Condensed Balance Sheet [Line Items]
Accrued Salaries, Current	33.6	49.9
Interest Payable, Current	47.5	48.5
Other Accrued Liabilities, Current	119.6	123.4
Assets:
Cash and cash equivalents	135.2	168.2
Other receivables, net	337.6	266.0
Other Receivables, Net, Current	24.6	19.4
Inventories, net	610.5	496.3
Property, Plant and Equipment including Oil and Gas Property, Net	503.9	503.1
Goodwill (Note 12)	2,280.2	2,277.1
Intangibles, net	1,589.5	1,612.0
Deferred charges and other assets	60.6	43.5
Disposal Group, Including Discontinued Operation, Assets, Noncurrent		1,376.9
Disposal Group, Including Discontinued Operation, Assets, Current	1,976.0	603.0
Assets	7,576.8	7,419.7
Liabilities and Equity:
Short-term Debt	20.3	19.4
Long-term Debt, Excluding Current Maturities	4,314.4	3,752.3
Employee benefit obligations	33.1	34.4
Deferred tax liabilities	285.8	493.2
Other liabilities	98.8	23.6
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		156.1
Disposal Group, Including Discontinued Operation, Liabilities, Current	558.6	500.6
Stockholders' Equity Attributable to Parent	1,051.7	1,095.4
Noncontrolling interests	653.8	751.3
Total permanent equity	1,705.5	1,846.7
Total liabilities and equity	7,576.8	7,419.7
Assets, Current	3,142.6	1,607.1
Prepaid Expense and Other Assets	58.7	54.2
Accounts Payable, Current	359.6	371.6
Liabilities, Current	1,139.2	1,113.4
Liabilities	5,871.3	5,573.0
Corporate and Other and eliminations [Member]
Condensed Balance Sheet [Line Items]
Accrued Salaries, Current	7.7	5.5
Interest Payable, Current	15.1	29.5
Other Accrued Liabilities, Current	9.4	2.4
Assets:
Cash and cash equivalents	623.6	101.9
Other receivables, net	0.0	0.0
Other Receivables, Net, Current	37.6	0.3
Inventories, net	0.0	0.0
Property, Plant and Equipment including Oil and Gas Property, Net	0.6	0.8
Goodwill (Note 12)	0.0	0.0
Intangibles, net	0.0	0.0
Deferred charges and other assets	0.2	0.2
Disposal Group, Including Discontinued Operation, Assets, Current	0.0	0.0
Assets	663.5	103.8
Liabilities and Equity:
Short-term Debt	50.0	142.0
Long-term Debt, Excluding Current Maturities	934.0	1,791.4
Employee benefit obligations	5.7	4.2
Deferred tax liabilities	0.0	0.0
Other liabilities	2.3	2.6
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		0.0
Disposal Group, Including Discontinued Operation, Liabilities, Current	0.0	0.0
Stockholders' Equity Attributable to Parent	(360.1)	(1,873.7)
Noncontrolling interests	(1.7)	(1.6)
Total permanent equity	(361.8)	(1,875.3)
Total liabilities and equity	663.5	103.8
Assets, Current	662.7	102.8
Prepaid Expense and Other Assets	1.5	0.6
Accounts Payable, Current	1.1	1.5
Liabilities, Current	83.3	180.9
Liabilities	1,025.3	1,979.1
Discontinued Operations, Held-for-sale [Member]
Condensed Balance Sheet [Line Items]
Accrued Salaries, Current		0.0
Interest Payable, Current		0.0
Other Accrued Liabilities, Current		0.0
Assets:
Disposal Group, Including Discontinued Operation, Assets, Noncurrent		0.0
Disposal Group, Including Discontinued Operation, Assets, Current		28,326.2
Assets		28,326.2
Liabilities and Equity:
Long-term Debt, Excluding Current Maturities		0.0
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		0.0
Disposal Group, Including Discontinued Operation, Liabilities, Current		26,350.7
Stockholders' Equity Attributable to Parent		1,536.3
Noncontrolling interests		439.2
Total permanent equity		1,975.5
Total liabilities and equity		28,326.2
Assets, Current		28,326.2
Liabilities, Current		26,350.7
Liabilities		26,350.7
Consolidated Entities
Condensed Balance Sheet [Line Items]
Accrued Salaries, Current	41.3	55.4
Interest Payable, Current	62.6	78.0
Other Accrued Liabilities, Current	129.0	125.8
Assets:
Cash and cash equivalents	758.8	270.1
Other receivables, net	337.6	266.0
Other Receivables, Net, Current	62.2	19.7
Inventories, net	610.5	496.3
Property, Plant and Equipment including Oil and Gas Property, Net	504.5	503.9
Goodwill (Note 12)	2,280.2	2,277.1
Intangibles, net	1,589.5	1,612.0
Deferred charges and other assets	60.8	43.7
Disposal Group, Including Discontinued Operation, Assets, Noncurrent		1,376.9
Disposal Group, Including Discontinued Operation, Assets, Current	1,976.0	28,929.2
Assets	8,240.3	35,849.7
Liabilities and Equity:
Short-term Debt	70.3	161.4
Long-term Debt, Excluding Current Maturities	5,248.4	5,543.7
Employee benefit obligations	38.8	38.6
Deferred tax liabilities	285.8	493.2
Other liabilities	101.1	26.2
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		156.1
Disposal Group, Including Discontinued Operation, Liabilities, Current	558.6	26,851.3
Stockholders' Equity Attributable to Parent	691.6	758.0
Noncontrolling interests	652.1	1,188.9
Total permanent equity	1,343.7	1,946.9
Total liabilities and equity	8,240.3	35,849.7
Assets, Current	3,805.3	30,036.1
Prepaid Expense and Other Assets	60.2	54.8
Accounts Payable, Current	360.7	373.1
Liabilities, Current	1,222.5	27,645.0
Liabilities	6,896.6	$ 33,902.8
Asset Management segment [Member]
Condensed Balance Sheet [Line Items]
Fair Value, Net Asset (Liability)	$ 70.3