Business Segments (Geographic Segment Information) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 3,323.0	$ 3,143.8	$ 2,960.9	$ 3,125.2	$ 3,683.0	$ 4,140.9	$ 3,845.0	$ 3,388.0	$ 12,552.9	$ 15,056.9	$ 9,199.6
Property, Plant and Equipment, Net	3,259.8				3,871.5				3,259.8	3,871.5
Russia
Segment Reporting Information [Line Items]
Revenues									2,773.3	4,894.2	283.3
Australia
Segment Reporting Information [Line Items]
Revenues									1,478.7	911.1	1,006.9
Property, Plant and Equipment, Net	325.8				408.3				325.8	408.3
Brazil
Segment Reporting Information [Line Items]
Revenues									1,275.8	1,534.7	1,033.7
Property, Plant and Equipment, Net	589.9				567.1				589.9	567.1
Norway
Segment Reporting Information [Line Items]
Revenues									1,202.6	971.2	574.4
Property, Plant and Equipment, Net	360.5				574.2				360.5	574.2
United States
Segment Reporting Information [Line Items]
Revenues									385.7	1,016.2	935.3
Malaysia
Segment Reporting Information [Line Items]
Property, Plant and Equipment, Net	311.4				321.4				311.4	321.4
United Kingdom
Segment Reporting Information [Line Items]
Revenues									926.6	953.9	776.6
Angola
Segment Reporting Information [Line Items]
Revenues									442.1	465.9	761.5
Property, Plant and Equipment, Net	925.6				1,190.1				925.6	1,190.1
All Other Countries
Segment Reporting Information [Line Items]
Revenues									4,068.1	4,309.7	$ 3,827.9
Property, Plant and Equipment, Net	$ 746.6				$ 810.4				$ 746.6	$ 810.4