Factbox - G20 finalises details of 'bail-in' bonds for big banks

LONDON (Reuters) - The Financial Stability Board (FSB) published its finalised new rule that will require the world's top 30 banks to issue bonds that can be written down to raise cash if they go bust. The aim is to avoid a failed bank having to rely on taxpayers and avert a repeat of the market mayhem that followed the collapse of Lehman Brothers in 2008. The bonds are in addition to a bank's core capital requirements. The following are the main elements of the total loss-absorbing capacity (TLAC) reform which will apply to the 30 lenders, including Goldman Sachs, Deutsche Bank and HSBC, that the FSB deems to be globally systemically important banks or GSIBs: * GSIBs must meet a minimum TLAC requirement of at least 16 percent of the group's risk-weighted assets (RWAs) from January 2019, and at least 18 percent from January 2022. This scales back a draft proposal for TLAC of 16-20 percent of RWAs. * Minimum TLAC must also be at least 6 percent of the Basel III leverage ratio denominator from January 2019, and at least 6.75 percent from January 2022. * The FSB's TLAC rule is a minimum standard, meaning some countries can require banks to hold higher amounts' * GSIBs from emerging markets such as the four from China must meet the 16 percent of RWAs and 6 percent leverage ratio requirements no later than January 2025, and the 18 percent of RWAs and 6.75 percent leverage requirements by January 2028. This scraps an open ended exemption for GSIBs from emerging markets in earlier versions. * GSIBs from emerging markets will have to accelerate compliance with TLAC if corporate debt markets reach 55 percent of GDP in their economy, meaning it is big enough to absorb TLAC bonds issuance. * Subsidiaries of banks must hold 75-90 percent of the TLAC requirement for the consolidated group, unchanged from earlier versions despite lobbying by banks for this to be lowered. * Authorities in countries that host a GSIB subsidiary would need approval from the bank's home supervisor before writing down locally held TLAC. Host supervisors could decide to force foreign GSIB subsidiaries to hold more TLAC. * All bonds must be subordinated to qualify but subordination can be done on a statutory or contractual basis. FSB says European Union, where a third of GSIBs are based, is looking at whether a coordinated approach to subordination is needed. * Basel Committee of banking supervisors to consult on imposing curbs on the quantity of "TLAC" bonds issued by one banks can be held by another GSIB on its books. (Reporting by Huw Jones; Editing by Hugh Lawson and Tom Heneghan)