Accounting Policies (Fair Value Measurement) (Details) - Fair Value, Measurements, Recurring [Member] $ in Millions	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	$ 54.1
Total assets at fair value	54.1
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	54.1
Total assets at fair value	54.1
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	0.0
Total assets at fair value	0.0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	0.0
Total assets at fair value	$ 0.0