Accounting Policies (Fair Value Measurement) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	$ 54.1	$ 126.7
Restricted amounts held in escrow-long term		12.3
Total assets at fair value	54.1	139.0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	54.1	126.7
Restricted amounts held in escrow-long term		12.3
Total assets at fair value	54.1	139.0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	0.0	0.0
Restricted amounts held in escrow-long term		0.0
Total assets at fair value	0.0	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	0.0
Restricted amounts held in escrow-long term		0.0
Total assets at fair value	$ 0.0	$ 0.0