Derivatives - Notional Amounts of Foreign Currency Forward Contracts (Details) - Foreign currency contracts $ in Millions	Jun. 30, 2019 USD ($) item
Designated as hedges | Euro
Notional amounts of foreign currency forward contracts
Notional amounts	$ 372.5
Designated as hedges | British pound
Notional amounts of foreign currency forward contracts
Notional amounts	65.1
Designated as hedges | Canadian dollar
Notional amounts of foreign currency forward contracts
Notional amounts	97.8
Designated as hedges | Australian dollar
Notional amounts of foreign currency forward contracts
Notional amounts	39.5
Designated as hedges | Other
Notional amounts of foreign currency forward contracts
Notional amounts	77.9
Not designated as hedges | Euro
Notional amounts of foreign currency forward contracts
Notional amounts	295.0
Not designated as hedges | British pound
Notional amounts of foreign currency forward contracts
Notional amounts	81.0
Not designated as hedges | Canadian dollar
Notional amounts of foreign currency forward contracts
Notional amounts	72.2
Not designated as hedges | Indian rupee
Notional amounts of foreign currency forward contracts
Notional amounts	60.5
Not designated as hedges | Mexican peso
Notional amounts of foreign currency forward contracts
Notional amounts	34.7
Not designated as hedges | Australian dollar
Notional amounts of foreign currency forward contracts
Notional amounts	32.7
Not designated as hedges | Japanese yen
Notional amounts of foreign currency forward contracts
Notional amounts	29.5
Not designated as hedges | Brazilian real
Notional amounts of foreign currency forward contracts
Notional amounts	27.8
Not designated as hedges | Other
Notional amounts of foreign currency forward contracts
Notional amounts	$ 126.1
Number of currency exposures within 'Other' | item	20
Maximum individual currency exposure within 'Other'	$ 25.0