Fair Value Measurements (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets
Investments, Fair Value Disclosure	$ 340.3	$ 328.6	$ 247.3	$ 242.3
Fair Value, Inputs, Level 1 [Member] \| Fair Value, Recurring [Member]
Assets
Foreign currency forward contracts receivable	0.0	0.0
Loans Receivable, Fair Value Disclosure	0.0	0.0
Deferred compensation plan assets	0.0	0.0
Investments, Fair Value Disclosure	77.2	69.4
Mortgage Banking Derivative Assets	0.0	0.0
Total assets at fair value	77.2	69.4
Liabilities
Foreign currency forward contracts payable	0.0	0.0
Deferred compensation plan liabilities	0.0	0.0
Business Combination, Contingent Consideration, Liability	0.0	0.0
Mortgage Banking Derivative Liabilities	0.0	0.0
Total liabilities at fair value	0.0	0.0
Fair Value, Inputs, Level 2 [Member] \| Fair Value, Recurring [Member]
Assets
Foreign currency forward contracts receivable	13.1	10.5
Loans Receivable, Fair Value Disclosure	1,529.2	527.1
Deferred compensation plan assets	446.3	349.9
Investments, Fair Value Disclosure	0.0	0.0
Mortgage Banking Derivative Assets	0.0	0.0
Total assets at fair value	1,988.6	887.5
Liabilities
Foreign currency forward contracts payable	3.4	4.4
Deferred compensation plan liabilities	427.6	346.1
Business Combination, Contingent Consideration, Liability	0.0	0.0
Mortgage Banking Derivative Liabilities	0.0	0.0
Total liabilities at fair value	431.0	350.5
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Recurring [Member]
Assets
Foreign currency forward contracts receivable	0.0	0.0
Loans Receivable, Fair Value Disclosure	0.0	0.0
Deferred compensation plan assets	0.0	0.0
Investments, Fair Value Disclosure	59.3	34.4	11.5
Mortgage Banking Derivative Assets	87.1	36.1
Total assets at fair value	146.4	70.5
Liabilities
Foreign currency forward contracts payable	0.0	0.0
Deferred compensation plan liabilities	0.0	0.0
Business Combination, Contingent Consideration, Liability	85.7	148.5	$ 192.0
Mortgage Banking Derivative Liabilities	73.4	25.9
Total liabilities at fair value	$ 159.1	$ 174.4

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of liability recognized arising from contingent consideration in a business combination.

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Amount of actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Fair value portion of asset contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward contracts, and swaps.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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