Goodwill and Other Intangibles - Narrative (Detail) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Oct. 01, 2017	May 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	May 16, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense related to other intangible assets			$ 11.4	$ 8.8	$ 10.9
Goodwill acquired			78.3	11.8
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense related to other intangible assets			11.4	$ 8.8	$ 10.9
Estimated future amortization expense for 2018			17.5
Estimated future amortization expense for 2019			17.4
Estimated future amortization expense for 2020			17.3
Estimated future amortization expense for 2021			14.8
Estimated future amortization expense for 2022			$ 10.1
UBS Asset Management Fund Administration Servicing Business
Acquired Finite-Lived Intangible Assets [Line Items]
Purchase price	$ 190.8
Cash consideration	188.5
Contingent consideration	2.3
Goodwill acquired	78.3
Intangible assets acquired	$ 126.0
Aviate Global LLP
Acquired Finite-Lived Intangible Assets [Line Items]
Purchase price		$ 18.8
Goodwill acquired		$ 10.5
Intangible assets acquired						$ 5.8
Performance related adjustment period		3 years