Revenue Contract Balances (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Accounts receivable, net of allowance of $44.5 and $42.7, respectively	$ 4,247.7	$ 4,585.0
Accounts receivable, billable to clients	1,945.8	1,747.4
Contract assets	44.9	11.5
Contract liabilities (deferred revenue)	$ 510.8	$ 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.

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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.

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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.

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No definition available.

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