cumsum() on multi-index pandas dataframe

I have a multi-index dataframe that shows the sum of transactions on a monthly frequency.

I am trying to get a cumsum() on yearly basis that respects my 'mapid' and 'service' multi-index. However I don't know how to derive that data

combined_df = combined_df.groupby([pd.Grouper(freq='M'), 'provider', 'mapid', 'service']).sum()                                                 costdatetime   provider mapid   service                  2017-08-31 Amazon   10147.0 Monitor              0.41                            Storage             90.51                            Virtual Machine  11646.322017-09-30 Amazon   10147.0 Monitor              0.89                            Storage            226.06                            Virtual Machine  32624.912017-10-31 Amazon   10147.0 Monitor              0.17                            Storage            261.72                            Virtual Machine  36934.932017-11-30 Amazon   10147.0 Monitor              0.35                            Storage            269.06                            Virtual Machine  30790.70

I would like to derive the follow results