Other Financial Information (Narrative) (Details) $ in Millions	12 Months Ended
	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	$ (75.4)	$ 59.7	$ 87.9
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