Derivative Instruments and Fair Value Accounting - Assets and liabilities Measured at fair value on recurring basis (Details) - Fair value measurements, recurring - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Level 1
Assets:
Cash equivalents	$ 30.0	$ 124.9
Restricted cash	114.2	171.6
Level 1 | Other assets
Assets:
Assets, Fair Value Disclosure	144.2	296.5
Fair Value, Inputs, Level 2 [Member] | Accrued Liabilities [Member]
Assets:
Financial and Nonfinancial Liabilities, Fair Value Disclosure	19.5	12.9
Level 3
Assets:
Assets, Fair Value Disclosure	0.0
Interest Rate Swap [Member] | Fair Value, Inputs, Level 2 [Member] | Accrued Liabilities [Member]
Assets:
Derivative Liability	$ 19.5	$ 12.9