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General and significant accounting policies (Narrative) (Details) - USD ($) $ in Millions | Sep. 30, 2023 | Jul. 01, 2023 | Jun. 30, 2023 | Dec. 31, 2022 | Jan. 01, 2021
--- | --- | --- | --- | --- | ---
General and significant accounting policies [Line Items] |  |  |  |  |
Retained earnings | $ 51,510 |  |  | $ 48,305 |
Accumulated other comprehensive income (loss) (AOCI) | $ (11,518) |  |  | (10,185) |
Huatai Group |  |  |  |  |
General and significant accounting policies [Line Items] |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  | 64.20% |  |
Huatai Group |  |  |  |  |
General and significant accounting policies [Line Items] |  |  |  |  |
Subsidiary, Ownership Percentage, Parent | 69.60% | 69.60% |  |  |
Subsidiary, Ownership Percentage, Noncontrolling Owner |  | 30.40% |  |  |
Effect of Modified Retrospective Application Accounting Standards Update 2018-12 |  |  |  |  |
General and significant accounting policies [Line Items] |  |  |  |  |
Retained earnings |  |  |  | 29 | $ 52
Accumulated other comprehensive income (loss) (AOCI) |  |  |  | $ 8 | $ 1,800

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