Accounting Policies (Fair Value Measurement) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	$ 126.7	$ 58.8
Restricted amounts held in escrow-long term	12.3	63.4
Total assets at fair value	139.0	122.2
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	126.7	58.8
Restricted amounts held in escrow-long term	12.3	63.4
Total assets at fair value	139.0	122.2
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	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	0.0
Total assets at fair value	$ 0.0	$ 0.0