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Fair value of obligations measured on a recurring basis.

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Amount of purchases of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Fair Value of Financial Instruments (Acquisition-Related Contingent Consideration) (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, range of potential undiscounted earn-out liabilities, low	$ 48.0
Acquisition-related contingent consideration liabilities, range of potential undiscounted earn-out liabilities, high	179.0
Acquisition-related contingent consideration liabilities, net increase (decrease), measurement period adjustments	$ 6.1	$ (0.1)
Discount Rate [Member] \| Minimum [Member]
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, measurement input, discount rate	0.120
Discount Rate [Member] \| Maximum [Member]
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, measurement input, discount rate	0.200
Discount Rate [Member] \| Weighted Average [Member]
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, measurement input, discount rate	0.131
Earn-Out Liabilities [Member]
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, estimated fair value	$ 135.2	173.2
Acquisition-related contingent consideration liabilities, additions from new business combinations	7.2	45.2	$ 1.5
Acquisition-related contingent consideration liabilities, net increase (decrease), measurement period adjustments	2.1	(6.1)	5.0
Acquisition-related contingent consideration liabilities, net increase (decrease), fair value adjustments, expense (income)	3.1	51.0	17.5
Acquisition-related contingent consideration liabilities, payments	50.4	35.0	$ 23.1
Earn-Out Liabilities [Member] \| Mandatorily Redeemable Stock [Member]
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, net increase (decrease), fair value adjustments, expense (income)	1.0
Earn-Out Liabilities [Member] \| Other Current Liabilities [Member]
Fair Value, Financial Instruments Measured on a Recurring Basis [Line Items]
Acquisition-related contingent consideration liabilities, estimated fair value	$ 48.1	$ 54.1