Divestitures - Schedule of (loss) income for discontinued operations (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred Tax Assets, Valuation Allowance		$ 969.4				$ 555.4				$ 969.4	$ 555.4
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		(25.1)	$ 7.7	$ (62.7)	$ 250.4	44.5	$ (185.5)	$ (19.9)	$ (17.2)	170.3	(178.1)	$ (292.7)
Net Income (Loss) Attributable to Parent		(26.2)	2.1	(82.1)	212.2	(7.3)	(132.9)	(24.7)	(33.9)	106.0	(198.8)	(556.8)
Less: Net income attributable to noncontrolling interest										167.2	164.9	44.4
Net income (loss)		24.0	$ 39.8	$ (51.4)	$ 260.8	36.2	$ (93.0)	$ 15.9	$ 7.0	273.2	(33.9)	(512.4)
Other (expense) income, net										(5.0)	4.8	10.1
Interest Expense										(360.1)	(402.5)	(407.8)
Consolidated operating income										516.3	573.5	179.1
Costs and Expenses										4,492.2	4,475.1	4,574.7
Selling, acquisition, operating and general expenses										1,359.6	1,355.3	1,523.8
Insurance Segment [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Write-down of assets held for sale to fair value less costs to sell		(421.2)				(362.8)				(421.2)	(362.8)
Disposal Group, Including Discontinued Operation, Revenue										1,641.5	1,320.5
Disposal Group, Including Discontinued Operation, Benefits and other changes in policy reserves										925.9	893.9
Disposal Group, Including Discontinued Operation, General and Administrative Expense										148.2	127.9
Disposal Group, Including Discontinued Operation, Depreciation and Amortization										197.5	78.6
Disposal Group, Including Discontinued Operation, Operating Expense										1,271.6	1,100.4
Disposal Group, Including Discontinued Operation, Operating Income (Loss)										369.9	220.1
Disposal Group, Including Discontinued Operation, Interest Expense										24.4	22.0
Discontinued Operation, Provision for Loss (Gain) on Disposal, Net of Tax										58.4	362.8
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax										287.1	(164.7)
Discontinued Operation, Tax Effect of Discontinued Operation	[1]									116.8	54.2
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest										170.3	(218.9)
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest										43.7	19.0
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent										126.6	(237.9)
Insurance Segment [Member] | Insurance Premiums [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue										43.9	72.5
Insurance Segment [Member] | Net Investment Income
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue										1,050.7	985.9
Insurance Segment [Member] | Gain (Loss) on Investments [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue										377.4	131.6
Insurance Segment [Member] | Insurance and investment product fees [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue										169.5	130.5
Compass Production Partners G.P. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue											40.2	107.4
Discontinued Operation, Provision for Loss (Gain) on Disposal, Net of Tax											53.6	0.0
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax											40.8
Oil and Gas Production Expense											38.2	85.9
Gain (Loss) on Disposition of Oil and Gas Property											105.6	0.0
Equity Method Investment, Realized Gain (Loss) Upon Step Acquisition											0.0	141.2
Net Income (Loss) Attributable to Parent											40.7	(367.5)
Less: Net income attributable to noncontrolling interest											0.1	(1.1)
Net income (loss)										0.0		(368.6)
Other (expense) income, net											1.5	25.7
Interest Expense											(5.9)	(9.9)
Consolidated operating income											(114.0)	(525.6)
Costs and Expenses											154.2	633.0
Asset Impairment Charges											93.2	485.1
Selling, acquisition, operating and general expenses											22.8	62.0
FGL [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred Tax Assets, Valuation Allowance						94.7					94.7
Operating Loss Carryforwards, Valuation Allowance						$ 258.0					258.0
Disposal Group, Including Discontinued Operation, Write-down of assets held for sale to fair value less costs to sell		$ 402.2								402.2
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax											$ 15.2
Disposal Group, Including Discontinued Operation, Revenue												947.2
Disposal Group, Including Discontinued Operation, Benefits and other changes in policy reserves												649.0
Disposal Group, Including Discontinued Operation, General and Administrative Expense												124.9
Disposal Group, Including Discontinued Operation, Depreciation and Amortization												41.8
Disposal Group, Including Discontinued Operation, Operating Expense												815.7
Disposal Group, Including Discontinued Operation, Operating Income (Loss)												131.5
Disposal Group, Including Discontinued Operation, Interest Expense												23.6
Discontinued Operation, Provision for Loss (Gain) on Disposal, Net of Tax										$ (39.4)		0.0
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax												107.9
Discontinued Operation, Tax Effect of Discontinued Operation	[1]											32.0
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest												75.9
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Noncontrolling Interest												23.1
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent												52.8
FGL [Member] | Insurance Premiums [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue												59.9
FGL [Member] | Net Investment Income
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue												923.0
FGL [Member] | Gain (Loss) on Investments [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue												(128.8)
FGL [Member] | Insurance and investment product fees [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Revenue												$ 93.1

[1] (a) Included in the income tax expense for Fiscal 2016 was a $15.2 of income tax expense primarily related to the establishment of a deferred tax liability of $367.9 at September 30, 2016, which was a result of classifying the Company’s ownership interest in FGL as held for sale following the Anbang/FGL Merger Agreement, partially offset by the recognition of a $94.7 deferred tax asset related to realized capital losses primarily from the Compass Sale and $258.0 reduction of valuation allowances on HRG’s net operating and capital loss carryforwards expected to offset the FGL taxable gain at September 30, 2016. The remaining liability is expected to be offset by losses recognized in continuing operations except for $15.2 of estimated alternative minimum taxes. Based on the Company’s current intent to exercise the 338 Tax Election related to the FGL Merger, the Company reversed the previously recorded deferred tax liability and deferred tax asset valuation allowance reduction, which resulted in the recognition of a $15.2 income tax benefit in Fiscal 2017.