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Revision of Prior Period Financial Statements (Prior Period Revisions) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | ---
Mar. 31, 2021 | Jun. 30, 2021 | Sep. 30, 2021 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Statement of Cash Flows [Abstract] |  |  |  |  |  |
Net cash provided by operations | $ (408) | $ 750 | $ 2,074 | $ 3,516 | $ 3,382 | $ 2,361
Financing cash flows: |  |  |  |  |  |
Change in fiduciary liabilities | 190 | 1,277 | 1,919 | 1,183 | 955 | 1,025
Other lines | (451) | (1,491) | (2,046) |  | (1,880) | 3,306
Net cash used for financing activities | (261) | (214) | (127) | (1,297) | (925) | 4,331
Investing cash flows: |  |  |  |  |  |
Acquisitions, net of cash and cash held in a fiduciary capacity acquired | 0 | (350) | (384) | (859) | (647) | (4,229)
Other lines | (67) | (74) | (188) |  | (146) | (166)
Net cash used for investing activities | (67) | (424) | (572) | (1,164) | (793) | (4,395)
Effect of exchange rate changes on cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity | (36) | 38 | (243) | (355) | 511 | 135
Increase in changes on cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity | (772) | 150 | 1,132 | 700 | 2,175 | 2,432
Cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity at beginning of year | 10,674 | 10,674 | 10,674 | 10,674 | 8,499 | 6,067
Cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity at end of year | 9,902 | 10,824 | 11,806 | 11,374 | 10,674 | 8,499
Cash and cash equivalents |  |  |  | 1,752 | 2,089 | 1,155
Cash and cash equivalents held in a fiduciary capacity |  |  |  | 9,622 | 8,585 | 7,344
Total cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity | 9,902 | 10,824 | 11,806 | 11,374 | 10,674 | 8,499
As Reported |  |  |  |  |  |
Statement of Cash Flows [Abstract] |  |  |  |  |  |
Net cash provided by operations | (408) | 750 | 2,074 |  | 3,382 | 2,361
Financing cash flows: |  |  |  |  |  |
Change in fiduciary liabilities | 0 | 0 | 0 |  | 0 | 0
Other lines | (451) | (1,491) | (2,046) |  | (1,880) | 3,306
Net cash used for financing activities | (451) | (1,491) | (2,046) |  | (1,880) | 3,306
Investing cash flows: |  |  |  |  |  |
Acquisitions, net of cash and cash held in a fiduciary capacity acquired | 0 | (363) | (401) |  | (668) | (5,505)
Other lines | (67) | (74) | (188) |  | (146) | (166)
Net cash used for investing activities | (67) | (437) | (589) |  | (814) | (5,671)
Effect of exchange rate changes on cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity | (43) | (23) | (130) |  | 246 | 93
Increase in changes on cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity | (969) | (1,201) | (691) |  | 934 | 89
Cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity at beginning of year | 2,089 | 2,089 | 2,089 | 2,089 | 1,155 | 1,066
Cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity at end of year | 1,120 | 888 | 1,398 |  | 2,089 | 1,155
Total cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity | 1,120 | 888 | 1,398 |  | 2,089 | 1,155
Effect of Change |  |  |  |  |  |
Statement of Cash Flows [Abstract] |  |  |  |  |  |
Net cash provided by operations | 0 | 0 | 0 |  | 0 | 0
Financing cash flows: |  |  |  |  |  |
Change in fiduciary liabilities | 190 | 1,277 | 1,919 |  | 955 | 1,025
Other lines | 0 | 0 | 0 |  | 0 | 0
Net cash used for financing activities | 190 | 1,277 | 1,919 |  | 955 | 1,025
Investing cash flows: |  |  |  |  |  |
Acquisitions, net of cash and cash held in a fiduciary capacity acquired | 0 | 13 | 17 |  | 21 | 1,276
Other lines | 0 | 0 | 0 |  | 0 | 0
Net cash used for investing activities | 0 | 13 | 17 |  | 21 | 1,276
Effect of exchange rate changes on cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity | 7 | 61 | (113) |  | 265 | 42
Increase in changes on cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity | 197 | 1,351 | 1,823 |  | 1,241 | 2,343
Cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity at beginning of year | 8,585 | 8,585 | 8,585 | $ 8,585 | 7,344 | 5,001
Cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity at end of year | 8,782 | 9,936 | 10,408 |  | 8,585 | 7,344
Total cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity | $ 8,782 | $ 9,936 | $ 10,408 |  | $ 8,585 | $ 7,344

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