is tencent support this now ?
Tencent Cloud is indeed in the Bandwidth Alliance. You can find the press release here: https://www.cloudflare.com/en-in/press-releases/2019/cloudflare-partners-with-tencent-cloud-to-further-expand-bandwidth-alliance/
is there some detail document about this?
there is no document on tencent website
I think you need to ask Tencent’s sales/support team regarding bandwidth alliance, just to make sure.
Alliance partners usually don’t say much, but when I’ve asked a couple of them, they’ve told me that if I get charged for bandwidth, just let them know and they’ll reverse the charges. Others have done it automatically.
I suggest you contact Tencent Support and ask how they handle it.