remote default with no argument removes default
Running `dvc remote default` with no argument sets default remote to `None`.
According to [documentation](https://dvc.org/doc/command-reference/remote/default) this should show the default remote though.

Setting default remote:
```
>>dvc remote default my_remote
>>git diff
... 
+[core]
+remote = my_remote
...
```

This should query the default, but sets default to `None`:
```
>>dvc remote default
>>git diff
...
+[core]
+remote = None
```
DVC version: 0.66.11
OS: Ubuntu 18.04.2 LTS
Method: From repository


diff --git a/dvc/command/remote.py b/dvc/command/remote.py
index 9ff361fd6..8c6dbc3ef 100644
--- a/dvc/command/remote.py
+++ b/dvc/command/remote.py
@@ -48,9 +48,13 @@ class CmdRemoteModify(CmdRemoteConfig):
 
 class CmdRemoteDefault(CmdRemoteConfig):
     def run(self):
-        self.remote_config.set_default(
-            self.args.name, unset=self.args.unset, level=self.args.level
-        )
+        if self.args.name is None and not self.args.unset:
+            name = self.remote_config.get_default(level=self.args.level)
+            print(name)
+        else:
+            self.remote_config.set_default(
+                self.args.name, unset=self.args.unset, level=self.args.level
+            )
         return 0
 
 
diff --git a/dvc/remote/config.py b/dvc/remote/config.py
index 17f1ef4fd..dccad52ba 100644
--- a/dvc/remote/config.py
+++ b/dvc/remote/config.py
@@ -151,3 +151,8 @@ class RemoteConfig(object):
         self.config.set(
             Config.SECTION_CORE, Config.SECTION_CORE_REMOTE, name, level=level
         )
+
+    def get_default(self, level=None):
+        return self.config.get(
+            Config.SECTION_CORE, Config.SECTION_CORE_REMOTE, level=level
+        )
diff --git a/tests/func/test_remote.py b/tests/func/test_remote.py
index f589eb234..8e8f00dee 100644
--- a/tests/func/test_remote.py
+++ b/tests/func/test_remote.py
@@ -145,6 +145,13 @@ class TestRemoteDefault(TestDvc):
         self.assertEqual(default, None)
 
 
+def test_show_default(dvc_repo, capsys):
+    assert main(["remote", "default", "foo"]) == 0
+    assert main(["remote", "default"]) == 0
+    out, _ = capsys.readouterr()
+    assert out == "foo\\n"
+
+
 class TestRemoteShouldHandleUppercaseRemoteName(TestDvc):
     upper_case_remote_name = "UPPERCASEREMOTE"
 
['dvc/remote/config.py', 'dvc/command/remote.py', 'tests/func/test_remote.py']