Business Segments (Geographic Segment Information) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenue	$ 3,683.0	$ 4,140.9	$ 3,845.0	$ 3,388.0	$ 2,047.7	$ 2,375.7	$ 2,370.5	$ 2,405.7	$ 15,056.9	$ 9,199.6	$ 11,471.9
Long-lived assets	3,871.5				2,620.1				3,871.5	2,620.1
Russia
Segment Reporting Information [Line Items]
Revenue									4,894.2	283.3	0.0
United States
Segment Reporting Information [Line Items]
Revenue									1,534.7	1,033.7	1,402.5
Long-lived assets	567.1				44.1				567.1	44.1
Angola
Segment Reporting Information [Line Items]
Revenue									1,016.2	935.3	1,013.7
Norway
Segment Reporting Information [Line Items]
Revenue									971.2	574.4	1,293.3
Long-lived assets	321.4				121.9				321.4	121.9
Malaysia
Segment Reporting Information [Line Items]
Long-lived assets	257.1				166.3				257.1	166.3
Brazil
Segment Reporting Information [Line Items]
Revenue									911.1	1,006.9	1,102.3
Long-lived assets	408.3				319.5				408.3	319.5
Australia
Segment Reporting Information [Line Items]
Revenue									953.9	776.6	1,044.8
United Kingdom
Segment Reporting Information [Line Items]
Revenue									465.9	761.5	1,155.4
Long-lived assets	1,190.1				1,078.2				1,190.1	1,078.2
All Other Countries
Segment Reporting Information [Line Items]
Revenue									4,309.7	3,827.9	$ 4,459.9
Long-lived assets	$ 1,127.5				$ 890.1				$ 1,127.5	$ 890.1