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Goodwill and Acquired Client Relationships - Schedule of Changes in Acquired Client Relationships (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Net Book Value |  |  |
Beginning balance, net book value | $ 1,449.7 |  |
Intangible amortization and impairments | (114.8) | $ (86.4) | $ (110.2)
Ending balance, net book value | 1,309.9 | 1,449.7 |
Acquired Client Relationships (Net) |  |  |
Definite-lived |  |  |
Beginning balance, gross book value | 1,295.5 | 1,290.0 |
Beginning balance, accumulated amortization | (874.5) | (788.1) |
Beginning balance, net book value | 421.0 | 501.9 |
Intangible amortization and impairments | (114.4) | (86.4) |
Foreign currency translation | (3.0) | 5.5 |
Ending balance, gross book value | 1,292.5 | 1,295.5 | 1,290.0
Ending balance, accumulated amortization | (988.9) | (874.5) | (788.1)
Ending balance, net book value | 303.6 | 421.0 | 501.9
Indefinite-lived |  |  |
Beginning balance, net book value | 1,028.7 | 995.5 |
Intangible amortization and impairments | (0.4) | 0.0 |
Foreign currency translation | (22.0) | 33.2 |
Ending balance, net book value | 1,006.3 | 1,028.7 | 995.5
Net Book Value |  |  |
Beginning balance, net book value | 1,449.7 | 1,497.4 |
Intangible amortization and impairments | (114.8) | (86.4) |
Foreign currency translation | (25.0) | 38.7 |
Ending balance, net book value | $ 1,309.9 | $ 1,449.7 | $ 1,497.4

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