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Pay vs Performance Disclosure | 12 Months Ended
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Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($)
Pay vs Performance Disclosure [Table] |  |  |
Pay vs Performance [Table Text Block] | PAY VERSUS PERFORMANCE One of the key principles by which we govern our executive compensat i on program is to support a strong performance culture through short-term and long-term variable compensation. In 2022, performance-based compensation represented 83% or more of each of our named executive officers’ target total direct compensation. As a result of this weighting toward variable, performance-based compensation, the financial performance of the Company, including stock performance, plays an integral role in deter min ing the compensation actually paid to each of our named executive officers each year.
Fiscal Year (a) |  | Summary Compensation Table Total for PEO (1) (b) |  |  | Compensation Actually Paid to PEO (2) (c) |  |  | Average Summary Compensation Table Total for Non-PEO NEOs (1) (d) |  |  | Average Compensation Actually Paid to Non-PEO NEOs (2) (e) |  |  | Value of Initial Fixed $100 Investment Based on : |  |  | Net Income (h) |  |  | Adjusted EPS Growth as Further Adjusted for Executive Compensation Purposes (4) (i) |
| Total Shareholder Return (3) (f) |  |  | Peer Group Total Shareholder Return (3) (g) |
2022 |  |  | 30,924,435 |  |  |  | 23,167,779 |  |  |  | 8,088,411 |  |  |  | 6,256,275 |  |  |  | 156 |  |  |  | 135 |  |  |  | 3,050.0 |  |  |  | 14.6% |
2021 |  |  | 21,519,703 |  |  |  | 89,772,223 |  |  |  | 6,997,689 |  |  |  | 21,130,889 |  |  |  | 161 |  |  |  | 152 |  |  |  | 3,143.0 |  |  |  | 20.5% |
2020 |  |  | 19,695,980 |  |  |  | 19,045,490 |  |  |  | 6,256,705 |  |  |  | 6,260,750 |  |  |  | 107 |  |  |  | 118 |  |  |  | 2,016.0 |  |  |  | 7.5% |
(1) | In 2020, 2021 and 2022, Dan Glaser was our Principal Executive Officer. Our other NEOs consisted of (i) for 2020 and 2021: Mark C. McGivney, John Q. Doyle, Peter C. Hearn and Martine Ferland; and (ii) for 2022: Mark C. McGivney, John Q. Doyle, Martin South and Martine Ferland.
(2) | Represe n ts the amount of “Compensation Actually Paid” to our NEOs as computed in accordance with Item 402(v) or Regulation S-K. The dollar amounts do not reflect the actual amount of compensation earned or paid to our NEOs during the applicable year. The following tables show the amounts deducted from and added to the Summary Compensation Table total for the PEO and for the average Summary Compensation Table Total for non-PEO NEOs.
PEO |
Fiscal Year |  | PEO Summary Compensation Table (SCT) Total |  |  | Additions/ (Subtractions) for Fair Value of Equity Awards Granted D uring Fiscal Year Reported in SCT (a) |  |  | Additions/ (Subtractions) for Change in Pension Value Reported in SCT (a) |  |  | Adjustments to PEO SCT Total (b) |  |  | PEO Compensation Actually Paid |
2022 |  |  | 30,924,435 |  |  |  | (21,613,490 | ) |  |  | 0 |  |  |  | 13,856,834 |  |  |  | 23,167,779 |
2021 |  |  | 21,519,703 |  |  |  | (12,778,669 | ) |  |  | 0 |  |  |  | 81,031,189 |  |  |  | 89,772,223 |
2020 |  |  | 19,695,980 |  |  |  | (11,927,984 | ) |  |  | (394,740 | ) |  |  | 11,672,235 |  |  |  | 19,045,490 |
Average Non-PEO NEOs |  |  |  |
Fiscal Year |  | Average Non-PEO Summary Compensation Table (SCT) Total |  |  | Additions/ (Subtractions) for Fair Value of Equity Awards Granted D uring Fiscal Year Reported in SCT (a) |  |  | Additions/ (Subtractions) for Change in Pension Value Reported in SCT (a) |  |  | Adjustments to Average Non-PEO SCT Total (b) |  |  | Average Non-PEO Compensation Actually Paid |
2022 |  |  | 8,088,411 |  |  |  | (3,308,939 | ) |  |  | 0 |  |  |  | 1,476,802 |  |  |  | 6,256,275 |
2021 |  |  | 6,997,689 |  |  |  | (2,709,151 | ) |  |  | (641 | ) |  |  | 16,842,992 |  |  |  | 21,130,889 |
2020 |  |  | 6,256,705 |  |  |  | (2,541,224 | ) |  |  | (53,245 | ) |  |  | 2,598,514 |  |  |  | 6,260,750 |
(a) | Includes the grant date fair value of stock awards and option awards, computed in accordance with FASB ASC Topic 718, as well as the aggregate change in the actuarial present value of the NEOs accumulated benefit under the Company’s defined benefit pension plans.
(b) | Includes the value of equity awards, calculated in accordance with Item 402(v) of Regulation S-K. The equity component of CAP is further detailed in the tables below for the Company’s PEO and average non-PEO NEOs, for fiscal years 2020, 2021 and 2022. We did not report a service cost or prior service cost for the Company’s pension plans.
PEO
Fiscal Year |  | Year-End Fair Value of Equity Awards Granted During the Fiscal Year that are Outstanding and Unvested |  |  | Change in Fair Value of Prior Year Awards that are Outstanding and Unvested |  |  | Change in Fair Value (from Prior Year-End) of Prior Year Awards that Vested During the Fiscal Year |  |  | Dividends Paid on Stock or Stock Option Awards Not Otherwise Reflected in Fair Value of Total Compensation |  |  | Total Adjustments |
2022 |  |  | 23,997,969 |  |  |  | (38,016,232 | ) |  |  | 27,462,921 |  |  |  | 412,176 |  |  |  | 13,856,834 |
2021 |  |  | 38,469,858 |  |  |  | 25,484,101 |  |  |  | 16,789,718 |  |  |  | 287,512 |  |  |  | 81,031,189 |
2020 |  |  | 10,984,767 |  |  |  | (22,729,414 | ) |  |  | 23,035,108 |  |  |  | 381,775 |  |  |  | 11,672,235 |
Average Non-PEO NEOs
Fiscal Year |  | Year-End Fair Value of Equity Awards Granted During the Fiscal Year that are Outstanding and Unvested |  |  | Change in Fair Value of Prior Year Awards that are Outstanding and Unvested |  |  | Change in Fair Value (from Prior Year-End) of Prior Year Awards that Vested During the Fiscal Year |  |  | Dividends Paid on Stock or Stock Option Awards Not Otherwise Reflected in Fair Value of Total Compensation |  |  | Total Adjustments |
2022 |  |  | 5,307,162 |  |  |  | (9,121,282 | ) |  |  | 5,198,788 |  |  |  | 92,134 |  |  |  | 1,476,802 |
2021 |  |  | 8,155,842 |  |  |  | 5,887,063 |  |  |  | 2,751,608 |  |  |  | 48,479 |  |  |  | 16,842,992 |
2020 |  |  | 2,340,307 |  |  |  | (3,500,643 | ) |  |  | 3,681,854 |  |  |  | 76,996 |  |  |  | 2,598,514 |
(3) | Reflects cumulative total stockholder return assuming $100 invested in the Company’s common stock versus the S&P 500 ® index on December 31, 2019 with dividends reinvested. The peer group used for this purpose is the S&P 500 ® index.
(4) | Adjusted EPS as further adjusted for executive compensation purposes is a non-GAAP measure. For the definition, please refer to the “Definitions of Financial Performance Measures” section on page 51 of the Compensation Discussion and Analysis.
Company Selected Measure Name | Adjusted EPS |  |
Named Executive Officers, Footnote [Text Block] | NEOs consisted of (i) for 2020 and 2021: Mark C. McGivney, John Q. Doyle, Peter C. Hearn and Martine Ferland; and (ii) for 2022: Mark C. McGivney, John Q. Doyle, Martin South and Martine Ferland. |  |
Peer Group Issuers, Footnote [Text Block] | Reflects cumulative total stockholder return assuming $100 invested in the Company’s common stock versus the S&P 500 ® index on December 31, 2019 with dividends reinvested. The peer group used for this purpose is the S&P 500 ® index. |  |
PEO Total Compensation Amount | $ 30,924,435 | $ 21,519,703 | $ 19,695,980
PEO Actually Paid Compensation Amount | $ 23,167,779 | 89,772,223 | 19,045,490
Adjustment To PEO Compensation, Footnote [Text Block] |
(2) | Represe n ts the amount of “Compensation Actually Paid” to our NEOs as computed in accordance with Item 402(v) or Regulation S-K. The dollar amounts do not reflect the actual amount of compensation earned or paid to our NEOs during the applicable year. The following tables show the amounts deducted from and added to the Summary Compensation Table total for the PEO and for the average Summary Compensation Table Total for non-PEO NEOs.
PEO |
Fiscal Year |  | PEO Summary Compensation Table (SCT) Total |  |  | Additions/ (Subtractions) for Fair Value of Equity Awards Granted D uring Fiscal Year Reported in SCT (a) |  |  | Additions/ (Subtractions) for Change in Pension Value Reported in SCT (a) |  |  | Adjustments to PEO SCT Total (b) |  |  | PEO Compensation Actually Paid |
2022 |  |  | 30,924,435 |  |  |  | (21,613,490 | ) |  |  | 0 |  |  |  | 13,856,834 |  |  |  | 23,167,779 |
2021 |  |  | 21,519,703 |  |  |  | (12,778,669 | ) |  |  | 0 |  |  |  | 81,031,189 |  |  |  | 89,772,223 |
2020 |  |  | 19,695,980 |  |  |  | (11,927,984 | ) |  |  | (394,740 | ) |  |  | 11,672,235 |  |  |  | 19,045,490 |
Average Non-PEO NEOs |  |  |  |
Fiscal Year |  | Average Non-PEO Summary Compensation Table (SCT) Total |  |  | Additions/ (Subtractions) for Fair Value of Equity Awards Granted D uring Fiscal Year Reported in SCT (a) |  |  | Additions/ (Subtractions) for Change in Pension Value Reported in SCT (a) |  |  | Adjustments to Average Non-PEO SCT Total (b) |  |  | Average Non-PEO Compensation Actually Paid |
2022 |  |  | 8,088,411 |  |  |  | (3,308,939 | ) |  |  | 0 |  |  |  | 1,476,802 |  |  |  | 6,256,275 |
2021 |  |  | 6,997,689 |  |  |  | (2,709,151 | ) |  |  | (641 | ) |  |  | 16,842,992 |  |  |  | 21,130,889 |
2020 |  |  | 6,256,705 |  |  |  | (2,541,224 | ) |  |  | (53,245 | ) |  |  | 2,598,514 |  |  |  | 6,260,750 |
(a) | Includes the grant date fair value of stock awards and option awards, computed in accordance with FASB ASC Topic 718, as well as the aggregate change in the actuarial present value of the NEOs accumulated benefit under the Company’s defined benefit pension plans.
PEO
Fiscal Year |  | Year-End Fair Value of Equity Awards Granted During the Fiscal Year that are Outstanding and Unvested |  |  | Change in Fair Value of Prior Year Awards that are Outstanding and Unvested |  |  | Change in Fair Value (from Prior Year-End) of Prior Year Awards that Vested During the Fiscal Year |  |  | Dividends Paid on Stock or Stock Option Awards Not Otherwise Reflected in Fair Value of Total Compensation |  |  | Total Adjustments |
2022 |  |  | 23,997,969 |  |  |  | (38,016,232 | ) |  |  | 27,462,921 |  |  |  | 412,176 |  |  |  | 13,856,834 |
2021 |  |  | 38,469,858 |  |  |  | 25,484,101 |  |  |  | 16,789,718 |  |  |  | 287,512 |  |  |  | 81,031,189 |
2020 |  |  | 10,984,767 |  |  |  | (22,729,414 | ) |  |  | 23,035,108 |  |  |  | 381,775 |  |  |  | 11,672,235 |
Average Non-PEO NEOs
Fiscal Year |  | Year-End Fair Value of Equity Awards Granted During the Fiscal Year that are Outstanding and Unvested |  |  | Change in Fair Value of Prior Year Awards that are Outstanding and Unvested |  |  | Change in Fair Value (from Prior Year-End) of Prior Year Awards that Vested During the Fiscal Year |  |  | Dividends Paid on Stock or Stock Option Awards Not Otherwise Reflected in Fair Value of Total Compensation |  |  | Total Adjustments |
2022 |  |  | 5,307,162 |  |  |  | (9,121,282 | ) |  |  | 5,198,788 |  |  |  | 92,134 |  |  |  | 1,476,802 |
2021 |  |  | 8,155,842 |  |  |  | 5,887,063 |  |  |  | 2,751,608 |  |  |  | 48,479 |  |  |  | 16,842,992 |
2020 |  |  | 2,340,307 |  |  |  | (3,500,643 | ) |  |  | 3,681,854 |  |  |  | 76,996 |  |  |  | 2,598,514 |
Non-PEO NEO Average Total Compensation Amount | $ 8,088,411 | 6,997,689 | 6,256,705
Non-PEO NEO Average Compensation Actually Paid Amount | $ 6,256,275 | 21,130,889 | 6,260,750
Adjustment to Non-PEO NEO Compensation Footnote [Text Block] |
(2) | Represe n ts the amount of “Compensation Actually Paid” to our NEOs as computed in accordance with Item 402(v) or Regulation S-K. The dollar amounts do not reflect the actual amount of compensation earned or paid to our NEOs during the applicable year. The following tables show the amounts deducted from and added to the Summary Compensation Table total for the PEO and for the average Summary Compensation Table Total for non-PEO NEOs.
PEO |
Fiscal Year |  | PEO Summary Compensation Table (SCT) Total |  |  | Additions/ (Subtractions) for Fair Value of Equity Awards Granted D uring Fiscal Year Reported in SCT (a) |  |  | Additions/ (Subtractions) for Change in Pension Value Reported in SCT (a) |  |  | Adjustments to PEO SCT Total (b) |  |  | PEO Compensation Actually Paid |
2022 |  |  | 30,924,435 |  |  |  | (21,613,490 | ) |  |  | 0 |  |  |  | 13,856,834 |  |  |  | 23,167,779 |
2021 |  |  | 21,519,703 |  |  |  | (12,778,669 | ) |  |  | 0 |  |  |  | 81,031,189 |  |  |  | 89,772,223 |
2020 |  |  | 19,695,980 |  |  |  | (11,927,984 | ) |  |  | (394,740 | ) |  |  | 11,672,235 |  |  |  | 19,045,490 |
Average Non-PEO NEOs |  |  |  |
Fiscal Year |  | Average Non-PEO Summary Compensation Table (SCT) Total |  |  | Additions/ (Subtractions) for Fair Value of Equity Awards Granted D uring Fiscal Year Reported in SCT (a) |  |  | Additions/ (Subtractions) for Change in Pension Value Reported in SCT (a) |  |  | Adjustments to Average Non-PEO SCT Total (b) |  |  | Average Non-PEO Compensation Actually Paid |
2022 |  |  | 8,088,411 |  |  |  | (3,308,939 | ) |  |  | 0 |  |  |  | 1,476,802 |  |  |  | 6,256,275 |
2021 |  |  | 6,997,689 |  |  |  | (2,709,151 | ) |  |  | (641 | ) |  |  | 16,842,992 |  |  |  | 21,130,889 |
2020 |  |  | 6,256,705 |  |  |  | (2,541,224 | ) |  |  | (53,245 | ) |  |  | 2,598,514 |  |  |  | 6,260,750 |
(a) | Includes the grant date fair value of stock awards and option awards, computed in accordance with FASB ASC Topic 718, as well as the aggregate change in the actuarial present value of the NEOs accumulated benefit under the Company’s defined benefit pension plans.
(b) | Includes the value of equity awards, calculated in accordance with Item 402(v) of Regulation S-K. The equity component of CAP is further detailed in the tables below for the Company’s PEO and average non-PEO NEOs, for fiscal years 2020, 2021 and 2022. We did not report a service cost or prior service cost for the Company’s pension plans.
PEO
Fiscal Year |  | Year-End Fair Value of Equity Awards Granted During the Fiscal Year that are Outstanding and Unvested |  |  | Change in Fair Value of Prior Year Awards that are Outstanding and Unvested |  |  | Change in Fair Value (from Prior Year-End) of Prior Year Awards that Vested During the Fiscal Year |  |  | Dividends Paid on Stock or Stock Option Awards Not Otherwise Reflected in Fair Value of Total Compensation |  |  | Total Adjustments |
2022 |  |  | 23,997,969 |  |  |  | (38,016,232 | ) |  |  | 27,462,921 |  |  |  | 412,176 |  |  |  | 13,856,834 |
2021 |  |  | 38,469,858 |  |  |  | 25,484,101 |  |  |  | 16,789,718 |  |  |  | 287,512 |  |  |  | 81,031,189 |
2020 |  |  | 10,984,767 |  |  |  | (22,729,414 | ) |  |  | 23,035,108 |  |  |  | 381,775 |  |  |  | 11,672,235 |
Average Non-PEO NEOs
Fiscal Year |  | Year-End Fair Value of Equity Awards Granted During the Fiscal Year that are Outstanding and Unvested |  |  | Change in Fair Value of Prior Year Awards that are Outstanding and Unvested |  |  | Change in Fair Value (from Prior Year-End) of Prior Year Awards that Vested During the Fiscal Year |  |  | Dividends Paid on Stock or Stock Option Awards Not Otherwise Reflected in Fair Value of Total Compensation |  |  | Total Adjustments |
2022 |  |  | 5,307,162 |  |  |  | (9,121,282 | ) |  |  | 5,198,788 |  |  |  | 92,134 |  |  |  | 1,476,802 |
2021 |  |  | 8,155,842 |  |  |  | 5,887,063 |  |  |  | 2,751,608 |  |  |  | 48,479 |  |  |  | 16,842,992 |
2020 |  |  | 2,340,307 |  |  |  | (3,500,643 | ) |  |  | 3,681,854 |  |  |  | 76,996 |  |  |  | 2,598,514 |
Compensation Actually Paid vs. Total Shareholder Return [Text Block] | COMPENSATION ACTUALLY PAID ( CAP ) (Dollars in Millions) |  |
Compensation Actually Paid vs. Net Income [Text Block] | NET INCOME (Dollars in Millions) |  |
Compensation Actually Paid vs. Company Selected Measure [Text Block] | PEO AND NON - PEO CAP VS . ADJUSTED EPS GROWTH (Dollars in Millions) |  |
Total Shareholder Return Vs Peer Group [Text Block] | TSR VS. PEER GROUP |  |
Tabular List [Table Text Block] |
Most Important Performance Measures (3 to 7 metrics without ranking)
TSR
Adjusted EPS as further adjusted for executive compensation purposes
Operating NOI growth
Total Shareholder Return Amount | $ 156 | 161 | 107
Peer Group Total Shareholder Return Amount | 135 | 152 | 118
Net Income (Loss) | $ 3,050,000,000 | $ 3,143,000,000 | $ 2,016,000,000
Company Selected Measure Amount | 14.6 | 20.5 | 7.5
PEO Name | Dan Glaser |  |
Measure [Axis]: 1 |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Measure Name | TSR |  |
Measure [Axis]: 2 |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Measure Name | Adjusted EPS as further adjusted for executive compensation purposes |  |
Non-GAAP Measure Description [Text Block] | Adjusted EPS as further adjusted for executive compensation purposes is a non-GAAP measure. For the definition, please refer to the “Definitions of Financial Performance Measures” section on page 51 of the Compensation Discussion and Analysis. |  |
Measure [Axis]: 3 |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Measure Name | Operating NOI growth |  |
Fair Value of Equity Awards Granted During Fiscal Year Reported in SCT [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | $ (3,308,939) | $ (2,709,151) | $ (2,541,224)
PEO [Member] | Fair Value of Equity Awards Granted During Fiscal Year Reported in SCT [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | (21,613,490) | (12,778,669) | (11,927,984)
PEO [Member] | Change in Pension Value Reported in SCT [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 0 | 0 | (394,740)
PEO [Member] | Adjustments to Peo Sct Total [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 13,856,834 | 81,031,189 | 11,672,235
PEO [Member] | Year End Fair Value of Equity Awards Granted During the Fiscal Year that are Outstanding and Unvested [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 23,997,969 | 38,469,858 | 10,984,767
PEO [Member] | Change in Fair Value of Prior Year Awards that are Outstanding and Unvested [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | (38,016,232) | 25,484,101 | (22,729,414)
PEO [Member] | Change in Fair Value (from Prior YearEnd) of Prior Year Awards that Vested During the Fiscal Year [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 27,462,921 | 16,789,718 | 23,035,108
PEO [Member] | Dividends Paid on Stock or Stock Option Awards Not Otherwise Reflected in Fair Value of Total Compensation [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 412,176 | 287,512 | 381,775
PEO [Member] | Total Adjustments [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 13,856,834 | 81,031,189 | 11,672,235
Non-PEO NEO [Member] | Change in Pension Value Reported in SCT [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 0 | (641) | (53,245)
Non-PEO NEO [Member] | Adjustments to Peo Sct Total [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 1,476,802 | 16,842,992 | 2,598,514
Non-PEO NEO [Member] | Year End Fair Value of Equity Awards Granted During the Fiscal Year that are Outstanding and Unvested [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 5,307,162 | 8,155,842 | 2,340,307
Non-PEO NEO [Member] | Change in Fair Value of Prior Year Awards that are Outstanding and Unvested [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | (9,121,282) | 5,887,063 | (3,500,643)
Non-PEO NEO [Member] | Change in Fair Value (from Prior YearEnd) of Prior Year Awards that Vested During the Fiscal Year [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 5,198,788 | 2,751,608 | 3,681,854
Non-PEO NEO [Member] | Dividends Paid on Stock or Stock Option Awards Not Otherwise Reflected in Fair Value of Total Compensation [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | 92,134 | 48,479 | 76,996
Non-PEO NEO [Member] | Total Adjustments [Member] |  |  |
Pay vs Performance Disclosure [Table] |  |  |
Adjustment to Compensation Amount | $ 1,476,802 | $ 16,842,992 | $ 2,598,514

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