Contingencies and Off-Balance Sheet Commitments (Details) - USD ($) $ in Millions	1 Months Ended
	Oct. 31, 2014	Jun. 30, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Public liability and property damage		$ 384.0	$ 385.0
Litigation settlement, second amendment filing period	30 days
Concession Fee Recoveries
Loss Contingencies [Line Items]
Litigation settlement, amount	$ 42.0
Litigation settlement, interest	11.0
Litigation settlement, expense	3.1
Concession Fee Recoveries | Restitution Fund
Loss Contingencies [Line Items]
Litigation settlement, expense	$ 3.1