Accumulated Other Comprehensive Income - Tax Effects Allocated to Each Component of Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total other comprehensive income (loss)	$ 1.1
Foreign currency translation adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax	0.5	$ 0.8
Other comprehensive income (loss), tax benefit (expense)	0.0	0.0
Total other comprehensive income (loss)	0.5	0.8
Amortization related to derivative securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax	0.7	0.7
Other comprehensive income (loss), tax benefit (expense)	(0.1)	(0.1)
Total other comprehensive income (loss)	0.6	0.6
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), pre-tax	1.2	1.5
Other comprehensive income (loss), tax benefit (expense)	(0.1)	(0.1)
Total other comprehensive income (loss)	$ 1.1	$ 1.4

BrightSphere Investment Group plc 10-Q