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Employee Incentive Plans (Share Grants And Fair Value) (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended | 128 Months Ended | 164 Months Ended
--- | --- | --- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2020
Employee Incentive Plans [Abstract] |  |  |  |  |  |  |
Shares granted |  | 1,229,177 | [1] | 1,374,217 | 1,146,267 | 24,497,626 |
Fair Value - Date of Grant |  | $ 71 |  | $ 65 | $ 62 | $ 561 | $ 71
Shares Granted IPO to Date |  |  |  |  |  |  | 28,247,287
Fair Value - Date of Grant IPO to Date |  |  |  |  |  |  | $ 759
Stock Incentive Plan Granted Shares Adjustment | 7,034 |  |  |  |  |  |
[1] | Stock Incentive Plan number of granted restricted stock units related to 2020 was adjusted by 7,034 additional restricted stock units during the nine months ended September 30, 2021.

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- Definition Fair Value of shares granted under the 2007 Stock Incentive Plan. + References No definition available. + Details
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- Definition Fair Value of all shares granted under the 2007 Stock Incentive Plan from the IPO to date. + References No definition available. + Details
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- Definition Number of shares granted under the 2007 Stock Incentive Plan. + References No definition available. + Details
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