Earnings Per Common Share Shares Repurchase (Details) $ in Millions	Dec. 31, 2017 USD ($)
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 300.0
Class A Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchase Program, Authorized Amount	$ 300.0