Revenue Contract Balances (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accounts receivable, net of allowance of $43.1 and $42.7, respectively	$ 3,942.5	$ 4,585.0
Accounts receivable, billable to clients	1,981.1	1,747.4
Contract assets	26.6	11.5
Contract liabilities (deferred revenue)	$ 507.5	$ 484.7

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

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Amount received for services rendered and products shipped, but not yet billed, for non-contractual agreements due within one year or the normal operating cycle, if longer.

+ References

No definition available.

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