KeyError after merging dataframes with columns renamed from the same name
Not an error, just a typo.  Please ignore the below.

#### Code Sample, a copy-pastable example if possible

```python
keywords = keywords.rename(columns={'id':'keywordId'}
campaigns = campaigns.rename(columns={'id':'campaignId'}
combined = keywords.merge(campains, left_on='keywordFull', right_on='keyword', how='left')
combined['keywordId', 'campaignId']

```
#### Problem description
It appears that renaming columns from the same name and then referencing them directly causes an error.  I suspect that this is because both columns were originally named 'id'.

Note that simply executing `combined` or `combined.head()` results in no issues.
```
KeyError: ('keywordId', 'campaignId')

c:\programdata\anaconda3\envs\bid2\lib\site-packages\pandas\core\frame.py in _getitem_column(self, key)
   2690         # get column
   2691         if self.columns.is_unique:
-> 2692             return self._get_item_cache(key)
   2693 
   2694         # duplicate columns & possible reduce dimensionality
``` 

#### Expected Output

#### Output of ``pd.show_versions()``

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.5.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 94 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.23.0
pytest: None
pip: 10.0.1
setuptools: 39.1.0
Cython: None
numpy: 1.14.3
scipy: 1.1.0
pyarrow: None
xarray: None
IPython: 6.4.0
sphinx: None
patsy: None
dateutil: 2.7.3
pytz: 2018.4
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.2.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: 4.2.1
bs4: None
html5lib: 1.0.1
sqlalchemy: 1.2.7
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: 0.5.0
pandas_datareader: None

</details>