Other Financial Information (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) item
Other Financial Information [Line Items]
Net gains (losses) from foreign currency transactions	$ (7.8)	$ (75.4)	$ 59.7
Deepwater rig contract exit costs				$ 282.0
Payment of contract exit costs			266.7
Write down of accrued contract exit costs		$ 6.1	$ 4.3
Gulf Of Mexico [Member]
Other Financial Information [Line Items]
Number of deepwater drilling rigs | item				2