Revenue (Tables)

12 Months Ended

Dec. 31, 2023

Revenue from Contract with Customer [Abstract]

Revenue from External Customers by Geographic Areas [Table Text Block]

	Years ended December 31,
Total revenue:	2023		2022		2021
United States	$	7,033.1	$	7,031.0	$	6,360.2
International:
United Kingdom	891.5		902.7		880.5
Continental Europe	901.3		867.5		892.8
Asia Pacific	868.3		918.5		970.1
Latin America	477.0		454.9		430.3
Other	718.1		753.2		706.8
Total International	3,856.2		3,896.8		3,880.5
Total Consolidated	$	10,889.3	$	10,927.8	$	10,240.7

	Years ended December 31,
Revenue before billable expenses:	2023		2022		2021
United States	$	6,102.2	$	6,157.7	$	5,763.1
International:
United Kingdom	759.2		742.2		781.5
Continental Europe	795.7		764.6		799.7
Asia Pacific	729.8		772.7		791.4
Latin America	448.7		423.6		396.4
Other	565.0		588.6		575.8
Total International	3,298.4		3,291.7		3,344.8
Total Consolidated	$	9,400.6	$	9,449.4	$	9,107.9

MD&E	Years ended December 31,
Total revenue:	2023		2022		2021
United States	$	2,731.4	$	2,730.2	$	2,584.7
International	1,663.4		1,651.4		1,611.9
Total MD&E	$	4,394.8	$	4,381.6	$	4,196.6
Revenue before billable expenses:
United States	$	2,703.5	$	2,690.9	$	2,552.0
International	1,623.0		1,606.0		1,565.7
Total MD&E	$	4,326.5	$	4,296.9	$	4,117.7

IA&C	Years ended December 31,
Total revenue:	2023		2022		2021
United States	$	2,508.8	$	2,585.9	$	2,403.3
International	1,493.4		1,554.7		1,638.5
Total IA&C	$	4,002.2	$	4,140.6	$	4,041.8
Revenue before billable expenses:
United States	$	2,383.8	$	2,483.7	$	2,306.0
International	1,249.4		1,282.6		1,373.7
Total IA&C	$	3,633.2	$	3,766.3	$	3,679.7

SC&E	Years ended December 31,
Total revenue:	2023		2022		2021
United States	$	1,792.9	$	1,714.9	$	1,372.2
International	699.4		690.7		630.1
Total SC&E	$	2,492.3	$	2,405.6	$	2,002.3
Revenue before billable expenses:
United States	$	1,014.9	$	983.1	$	905.1
International	426.0		403.1		405.4
Total SC&E	$	1,440.9	$	1,386.2	$	1,310.5

Contract with Customer, Asset and Liability [Table Text Block]

Contract Balances

The following table provides information about receivables, contract assets and contract liabilities from contracts with customers.

	December 31, 2023		December 31, 2022
Accounts receivable, net of allowance of $46.4 and $48.6, respectively	$	5,768.8	$	5,316.0
Accounts receivable, billable to clients	2,229.2		2,023.0
Contract assets	68.6		67.4
Contract liabilities (deferred revenue)	684.7		680.0