Divestitures - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operation, Provision for Loss (Gain) on Disposal, Net of Tax	$ 0.0	$ 0.0	$ 445.9	$ 0.0
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	0.7	(43.6)	501.5	259.2
Net income	(36.6)	(51.4)	$ 542.3	209.4
Document Period End Date			Mar. 31, 2018
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		$ 0.0	$ (445.9)	$ 0.0
Front Street RE (Cayman) Ltd. [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					$ (19.0)
Selling Expense			65.0
FGL [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					402.2
Selling Expense			1,518.3
GBA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Selling Expense			2,000.0
GBA [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Combination, Assets and Liabilities Arising from Contingencies, Amount Recognized, Net	100.0		100.0
HGI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Deferred Tax Assets, Valuation Allowance	441.2		441.2		$ 703.2
FS Holdco II Ltd. [Domain]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Combination, Assets and Liabilities Arising from Contingencies, Amount Recognized, Net	$ 26.6		$ 26.6
FGL [Member] | CF Corporation [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Acquisition, Share Price	$ 31.10		$ 31.10