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Basis of Preparation - Summary of impact of transition to IFRS 9 on retained earnings (Detail) - USD ($) $ in Millions | Jun. 30, 2018 | Jan. 01, 2018 | Dec. 31, 2017
--- | --- | --- | ---
Disclosure Of Financial Instruments [Line Items] |  |  |
Retained earnings | $ 23,755 |  | $ 23,761
Revaluation of funds |  | $ 1 |
IFRS 9 [Member] |  |  |
Disclosure Of Financial Instruments [Line Items] |  |  |
Retained earnings |  |  | $ 23,761
Costs of hedging adjustment |  | (22) |
Reclassification of equity investments from available for sale to FVPL |  | 12 |
Impairment provision resulting from the application of the ECL model |  | (7) |
Tax impact |  | 1 |
Revaluation of funds |  | 1 |
Adjustment to retained earnings from adoption of IFRS 9 on 1 January 2018 (sub-total) |  | (15) |
Retained Earnings 1 January 2018 IFRS 9 (Before Restatement for IFRS 15) [Member] | IFRS 9 [Member] |  |  |
Disclosure Of Financial Instruments [Line Items] |  |  |
Retained earnings |  | $ 23,746 |

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- Definition Impairment​ provision ​resulting​ from​ application​ of ECL model pre-tax. + References No definition available. + Details
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