Income Taxes - Operating Loss Carryforwards (Details) $ in Millions	Dec. 31, 2017 USD ($)
Operating Loss Carryforwards
Deferred tax asset relating to NOL carryforwards that have an indefinite life in several non U.S. jurisdictions	$ 1,710.0
Recognized valuation allowance relating to NOL carryforwards	1,700.0
Operating Loss Carryforwards
NOL carryforwards for state income tax purposes	744.0
U.S. Federal | Between 2019 and 2035
Operating Loss Carryforwards
Net operating loss carryforwards	398.0
Non U.S. Federal Jurisdictions
Operating Loss Carryforwards
Net operating loss carryforwards	7,100.0
Non U.S. Federal Jurisdictions | From 2016 to 2035
Operating Loss Carryforwards
Net operating loss carryforwards	550.0
State and Local Jurisdiction
Operating Loss Carryforwards
NOL carryforwards for alternative minimum tax purposes	$ 383.0