Goodwill and Other Intangibles - Narrative (Detail) - USD ($) $ in Millions		1 Months Ended		3 Months Ended	12 Months Ended
	Oct. 01, 2017	Nov. 30, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense related to other intangible assets					$ 17.4	$ 11.4	$ 8.8
Goodwill				$ 669.3	669.3	605.6	519.4
Goodwill acquired					71.4	78.3
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense related to other intangible assets					17.4	$ 11.4	$ 8.8
Estimated future amortization expense for 2019				16.8	16.8
Estimated future amortization expense for 2020				16.8	16.8
Estimated future amortization expense for 2021				14.4	14.4
Estimated future amortization expense for 2022				9.8	9.8
Estimated future amortization expense for 2023				9.5	9.5
BEx LLC
Acquired Finite-Lived Intangible Assets [Line Items]
Purchase price		$ 37.6
Cash consideration				31.2
Omnium Technology
Acquired Finite-Lived Intangible Assets [Line Items]
Purchase price			$ 73.0
Goodwill				71.4	71.4
Intangible assets acquired				$ 1.6	$ 1.6
UBS Asset Management Fund Administration Servicing Business
Acquired Finite-Lived Intangible Assets [Line Items]
Purchase price	$ 191.3
Goodwill	78.3
Intangible assets acquired	$ 126.0