Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019 |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | $ 3,742.2 | $ 5,373.1 | $ 8,361.3 | $ 10,418 |
Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 3,682.1 | 5,252.9 | 8,206.7 | 10,184.2 |
Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 60.1 | 120.2 | 154.6 | 233.8 |
Staffing and Interim | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 3,254.1 | 4,759.7 | 7,289.8 | 9,212.1 |
Outcome-Based Solutions and Consulting | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 326.4 | 369.3 | 700.4 | 728.1 |
Permanent Recruitment | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 86.4 | 158.9 | 219.7 | 308 |
Other | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 75.3 | 85.2 | 151.4 | 169.8 |
Americas | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 836.6 | 1,068.2 | 1,847.6 | 2,098.4 |
Americas | Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 826.4 | 1,050.2 | 1,820.7 | 2,063.4 |
Americas | Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 10.2 | 18 | 26.9 | 35 |
Americas | United States | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 515.9 | 652.7 | 1,126.8 | 1,275.9 |
Americas | United States | Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 507.6 | 639 | 1,105.4 | 1,249.2 |
Americas | United States | Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 8.3 | 13.7 | 21.4 | 26.7 |
Americas | Other Americas | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 320.7 | 415.5 | 720.8 | 822.5 |
Americas | Other Americas | Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 318.8 | 411.2 | 715.3 | 814.2 |
Americas | Other Americas | Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 1.9 | 4.3 | 5.5 | 8.3 |
Americas | Staffing and Interim | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 736.2 | 944.1 | 1,634.4 | 1,858.2 |
Americas | Staffing and Interim | United States | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 429 | 551.3 | 947.7 | 1,080 |
Americas | Staffing and Interim | Other Americas | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 307.2 | 392.8 | 686.7 | 778.2 |
Americas | Outcome-Based Solutions and Consulting | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 37.8 | 51.7 | 80.3 | 99.1 |
Americas | Outcome-Based Solutions and Consulting | United States | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 30.5 | 38.4 | 60.6 | 73.3 |
Americas | Outcome-Based Solutions and Consulting | Other Americas | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 7.3 | 13.3 | 19.7 | 25.8 |
Americas | Permanent Recruitment | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 18.9 | 30.3 | 49.4 | 59 |
Americas | Permanent Recruitment | United States | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 15.8 | 24.1 | 40.8 | 47 |
Americas | Permanent Recruitment | Other Americas | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 3.1 | 6.2 | 8.6 | 12 |
Americas | Other | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 43.7 | 42.1 | 83.5 | 82.1 |
Americas | Other | United States | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 40.6 | 38.9 | 77.7 | 75.6 |
Americas | Other | Other Americas | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 3.1 | 3.2 | 5.8 | 6.5 |
Southern Europe | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 1,470.8 | 2,394.3 | 3,415.5 | 4,503.1 |
Southern Europe | Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 1,453.6 | 2,358.6 | 3,367.2 | 4,432.4 |
Southern Europe | Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 17.2 | 35.7 | 48.3 | 70.7 |
Southern Europe | France | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 736 | 1,425.3 | 1,829.8 | 2,731.4 |
Southern Europe | France | Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 729.5 | 1,412.6 | 1,811.6 | 2,705 |
Southern Europe | France | Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 6.5 | 12.7 | 18.2 | 26.4 |
Southern Europe | Italy | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 268.5 | 394.4 | 596.2 | 750.8 |
Southern Europe | Italy | Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 264.1 | 384.6 | 584.1 | 731.6 |
Southern Europe | Italy | Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 4.4 | 9.8 | 12.1 | 19.2 |
Southern Europe | Other Southern Europe | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 466.3 | 574.6 | 989.5 | 1,020.9 |
Southern Europe | Other Southern Europe | Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 460 | 561.4 | 971.5 | 995.8 |
Southern Europe | Other Southern Europe | Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 6.3 | 13.2 | 18 | 25.1 |
Southern Europe | Staffing and Interim | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 1,299 | 2,182.8 | 3,020.3 | 4,084.3 |
Southern Europe | Staffing and Interim | France | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 663.4 | 1,345.7 | 1,661.7 | 2,570.2 |
Southern Europe | Staffing and Interim | Italy | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 255 | 365.2 | 562.1 | 695.2 |
Southern Europe | Staffing and Interim | Other Southern Europe | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 380.6 | 471.9 | 796.5 | 818.9 |
Southern Europe | Outcome-Based Solutions and Consulting | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 142.5 | 154 | 319.9 | 303.1 |
Southern Europe | Outcome-Based Solutions and Consulting | France | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 62.5 | 58.4 | 140.6 | 117.1 |
Southern Europe | Outcome-Based Solutions and Consulting | Italy | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 5 | 11.9 | 13.7 | 21.7 |
Southern Europe | Outcome-Based Solutions and Consulting | Other Southern Europe | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 75 | 83.7 | 165.6 | 164.3 |
Southern Europe | Permanent Recruitment | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 19.7 | 40.3 | 54.3 | 78.9 |
Southern Europe | Permanent Recruitment | France | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 7.4 | 13.6 | 19.9 | 28.1 |
Southern Europe | Permanent Recruitment | Italy | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 4.8 | 10.7 | 13 | 20.6 |
Southern Europe | Permanent Recruitment | Other Southern Europe | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 7.5 | 16 | 21.4 | 30.2 |
Southern Europe | Other | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 9.6 | 17.2 | 21 | 36.8 |
Southern Europe | Other | France | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 2.7 | 7.6 | 7.6 | 16 |
Southern Europe | Other | Italy | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 3.7 | 6.6 | 7.4 | 13.3 |
Southern Europe | Other | Other Southern Europe | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 3.2 | 3 | 6 | 7.5 |
Northern Europe | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 865.7 | 1,194.1 | 1,934.2 | 2,394.6 |
Northern Europe | Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 848.6 | 1,160.8 | 1,890 | 2,328.2 |
Northern Europe | Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 17.1 | 33.3 | 44.2 | 66.4 |
Northern Europe | Staffing and Interim | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 768.3 | 1,050.8 | 1,717.9 | 2,104.2 |
Northern Europe | Outcome-Based Solutions and Consulting | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 64.4 | 88.3 | 135.3 | 179.8 |
Northern Europe | Permanent Recruitment | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 19.6 | 38.2 | 50.9 | 76.3 |
Northern Europe | Other | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 13.4 | 16.8 | 30.1 | 34.3 |
APME | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 569.1 | 716.5 | 1,164 | 1,421.9 |
APME | Services transferred over time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 553.5 | 683.3 | 1,128.8 | 1,360.2 |
APME | Services transferred at a point in time | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 15.6 | 33.2 | 35.2 | 61.7 |
APME | Staffing and Interim | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 450.6 | 582 | 917.2 | 1,165.4 |
APME | Outcome-Based Solutions and Consulting | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 81.7 | 75.3 | 164.9 | 146.1 |
APME | Permanent Recruitment | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | 28.2 | 50.1 | 65.1 | 93.8 |
APME | Other | | | | |
Disaggregation of Revenue [Line Items] | | | | |
Revenue | $ 8.6 | $ 9.1 | $ 16.8 | $ 16.6 |