Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Mar. 17, 2020
Indefinite-lived intangible assets:
Balance at the beginning of the period					$ 2,495.5
Foreign currency translation					(0.9)
Balance at the end of the period			$ 2,476.6		2,476.6
Definite-lived intangible assets:
Foreign currency translation					(0.1)
Accumulated amortization, balance at the beginning of the period		$ (147.2)		$ (147.2)	(116.3)
Amortization				(8.6)	(14.7)
Foreign currency translation				2.7	0.1
Accumulated amortization, balance at the end of the period	$ (91.7)		(130.9)	(91.7)	(130.9)
Net intangible assets
Net intangible assets, balance at the beginning of the period		3,088.6		3,088.6	3,123.3
Amortization				(8.6)	(14.7)
Impairment				(390.2)	(18.0)
Foreign currency translation				(33.3)	(0.9)
Net intangible assets, balance at the end of the period	2,638.6		3,089.7	2,638.6	3,089.7
Goodwill
Goodwill, balance at the beginning of the period		1,504.3		1,504.3	1,478.0
Impairment				123.5
Foreign currency translation				(46.9)	(0.6)
Goodwill, balance at the end of the period	1,310.4		1,477.4	1,310.4	1,477.4
The amount of fair value greater than carrying value for goodwill						$ 123.5
Goodwill and intangible assets impairment	26.4		18.0	513.7	18.0
Indefinite-Lived Intangible Assets			2,476.6		2,476.6
Sale
Intangible assets, net	2,638.6	3,088.6	3,089.7	3,088.6	3,089.7	2,638.6
Future Amortization:
2020 (remainder of year)						3.7
2021						7.5
2022						7.5
2023						7.2
2024						5.9
Thereafter						39.6
Total						71.4
Geneva
Indefinite-lived intangible assets:
Disposal						17.9
Definite-lived intangible assets:
Disposal						17.9
Net intangible assets
Impairment				(17.9)
Goodwill
Disposal						(23.5)	$ (23.5)
Sale
Ownership sold (as a percent)							100.00%
Intangible assets, net							$ 17.9
Allocated goodwill						23.5	$ 23.5
Client relationships
Definite-lived intangible assets:
Balance at the beginning of the period		364.7		364.7	363.3
Impairment		92.6		119.0
Foreign currency translation				(3.3)
Balance at the end of the period	163.1		363.2	163.1	363.2
Client relationships | Geneva
Indefinite-lived intangible assets:
Disposal						79.3
Definite-lived intangible assets:
Disposal						79.3
Accumulated amortization, balance at the end of the period	61.4			61.4
VelocityShares ETNs
Goodwill
Goodwill and intangible assets impairment				26.4
Investment management agreements
Indefinite-lived intangible assets:
Balance at the beginning of the period		2,490.3		2,490.3
Impairment		263.5		(263.5)
Foreign currency translation				(32.5)
Balance at the end of the period	2,194.3			2,194.3
Goodwill
Indefinite-Lived Intangible Assets	2,194.3	2,490.3		2,194.3		2,194.3
Impairment		(263.5)		263.5
Trademarks
Indefinite-lived intangible assets:
Balance at the beginning of the period		380.8		380.8	380.8
Impairment		7.7		(7.7)
Foreign currency translation				(0.2)
Balance at the end of the period	372.9		380.8	372.9	380.8
Goodwill
Indefinite-Lived Intangible Assets	$ 372.9	380.8	$ 380.8	372.9	$ 380.8	$ 372.9
Impairment		$ (7.7)		$ 7.7