Note that the keychain security is a bit of an exception -- it's particularly strong, as it's protecting password data. (My favorite detail, not mentioned in the original white paper: To prevent the iCloud Keychain HSMs from being updated with a more lax policy, the smartcards that would have been required to update them were destroyed in a private ceremony involving a blender.)

Other data in iCloud is generally under less extreme levels of security. This isn't to say that it's insecure, merely that it's not as fanatically protected. Some of it may be accessible by resetting your account password.