ECB to release documents to defuse German court challenge

FRANKFURT (Reuters) - The European Central Bank agreed to give vital documents to German authorities to prove the proportionality of ECB policies, two sources said, in a step to defuse a challenge threatening to undermine its powers to keep the euro zone together.Germany's Constitutional Court ruled in May that the ECB overstepped its mandate with over 2 trillion euros of government bond purchases, ordering the Bundesbank to quit the scheme unless the ECB can prove proportionality within three..