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v3.19.3.a.u2

Summary of Significant Accounting Principles and Practices - Additional Information (Details) £ in Millions, $ in Millions | 12 Months Ended |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2019 GBP (£) | Jan. 01, 2020 USD ($) | Dec. 31, 2019 USD ($) | Jan. 01, 2019 USD ($) | Dec. 31, 2018 GBP (£) | Dec. 31, 2018 USD ($) | Jan. 01, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Cash and Cash Equivalents |  |  |  |  |  |  |  |  |
Cash and cash equivalents and short-term investments |  |  | $ 928.0 |  |  | $ 828.0 |  |  |
Restricted cash and investments, current |  |  | 110.0 |  |  | 91.0 |  |  |
Operating funds in U.K. | £ 42.7 |  | 55.5 |  | £ 42.7 | 53.9 |  |  |
Fiduciary Assets and Liabilities |  |  |  |  |  |  |  |  |
Premium trust balances |  |  | 5,200.0 |  |  | 3,900.0 |  |  |
Allowance for Doubtful Accounts |  |  |  |  |  |  |  |  |
Allowance for doubtful accounts |  |  | 70.0 |  |  | $ 62.0 |  | $ 59.0 | $ 56.0
New Accounting Pronouncements and Changes in Accounting Principles [Abstract] |  |  |  |  |  |  |  |  |
Operating lease right-of-use assets |  |  | 929.0 |  |  |  |  |  |
Present value of lease liabilities |  |  | $ 1,130.0 |  |  |  |  |  |
Adoption of new accounting guidance |  |  |  |  |  |  | $ 492.0 |  |
Buildings |  |  |  |  |  |  |  |  |
Fixed Assets |  |  |  |  |  |  |  |  |
Fixed assets, original life, weighted-average | 35 years |  |  |  |  |  |  |  |
Automobiles |  |  |  |  |  |  |  |  |
Fixed Assets |  |  |  |  |  |  |  |  |
Fixed assets, original life, weighted-average | 6 years |  |  |  |  |  |  |  |
Minimum | Software |  |  |  |  |  |  |  |  |
Fixed Assets |  |  |  |  |  |  |  |  |
Fixed assets, original life, weighted-average | 4 years |  |  |  |  |  |  |  |
Minimum | Furniture, fixtures and equipment |  |  |  |  |  |  |  |  |
Fixed Assets |  |  |  |  |  |  |  |  |
Fixed assets, original life, weighted-average | 4 years |  |  |  |  |  |  |  |
Minimum | Computer equipment |  |  |  |  |  |  |  |  |
Fixed Assets |  |  |  |  |  |  |  |  |
Fixed assets, original life, weighted-average | 4 years |  |  |  |  |  |  |  |
Maximum | Software |  |  |  |  |  |  |  |  |
Fixed Assets |  |  |  |  |  |  |  |  |
Fixed assets, original life, weighted-average | 7 years |  |  |  |  |  |  |  |
Maximum | Leasehold improvements |  |  |  |  |  |  |  |  |
Fixed Assets |  |  |  |  |  |  |  |  |
Fixed assets, original life, weighted-average | 10 years |  |  |  |  |  |  |  |
Maximum | Furniture, fixtures and equipment |  |  |  |  |  |  |  |  |
Fixed Assets |  |  |  |  |  |  |  |  |
Fixed assets, original life, weighted-average | 10 years |  |  |  |  |  |  |  |
Maximum | Computer equipment |  |  |  |  |  |  |  |  |
Fixed Assets |  |  |  |  |  |  |  |  |
Fixed assets, original life, weighted-average | 6 years |  |  |  |  |  |  |  |
Accounting Standards Update 2016-02 |  |  |  |  |  |  |  |  |
New Accounting Pronouncements and Changes in Accounting Principles [Abstract] |  |  |  |  |  |  |  |  |
Operating lease right-of-use assets |  |  |  | $ 1,100.0 |  |  |  |  |
Present value of lease liabilities |  |  |  | $ 1,300.0 |  |  |  |  |
Accounting Standards Update 2014-09 |  |  |  |  |  |  |  |  |
New Accounting Pronouncements and Changes in Accounting Principles [Abstract] |  |  |  |  |  |  |  |  |
Adoption of new accounting guidance |  |  |  |  |  |  | $ 507.0 |  |
Accounting Standards Update 2016-13 | Subsequent Event |  |  |  |  |  |  |  |  |
New Accounting Pronouncements and Changes in Accounting Principles [Abstract] |  |  |  |  |  |  |  |  |
Adoption of new accounting guidance |  | $ 10.0 |  |  |  |  |  |  |
Tradenames | Minimum |  |  |  |  |  |  |  |  |
Goodwill and Intangible Assets |  |  |  |  |  |  |  |  |
Useful life of finite-lived intangible assets | 1 year |  |  |  |  |  |  |  |
Tradenames | Maximum |  |  |  |  |  |  |  |  |
Goodwill and Intangible Assets |  |  |  |  |  |  |  |  |
Useful life of finite-lived intangible assets | 3 years |  |  |  |  |  |  |  |
Customer related and contract based | Minimum |  |  |  |  |  |  |  |  |
Goodwill and Intangible Assets |  |  |  |  |  |  |  |  |
Useful life of finite-lived intangible assets | 7 years |  |  |  |  |  |  |  |
Customer related and contract based | Maximum |  |  |  |  |  |  |  |  |
Goodwill and Intangible Assets |  |  |  |  |  |  |  |  |
Useful life of finite-lived intangible assets | 20 years |  |  |  |  |  |  |  |
Technology | Minimum |  |  |  |  |  |  |  |  |
Goodwill and Intangible Assets |  |  |  |  |  |  |  |  |
Useful life of finite-lived intangible assets | 5 years |  |  |  |  |  |  |  |
Technology | Maximum |  |  |  |  |  |  |  |  |
Goodwill and Intangible Assets |  |  |  |  |  |  |  |  |
Useful life of finite-lived intangible assets | 7 years |  |  |  |  |  |  |  |

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