Segment Information (Schedule Of Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 460.2	$ 548.2	$ 1,388.8	$ 2,271.8
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	285.8	298.1	855.2	1,012.0
Depreciation	108.2	109.4	325.3	335.1
General and administrative	30.4	25.3	86.9	76.1
OPERATING INCOME	35.8	115.4	121.4	848.6
Property and equipment, net	11,096.4	10,959.7	11,096.4	10,959.7	$ 10,919.3
Floaters
Segment Reporting Information [Line Items]
Revenues	291.9	319.3	840.7	1,468.3
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	139.1	153.7	431.1	573.6
Depreciation	72.7	72.9	217.5	231.0
General and administrative	0.0	0.0	0.0	0.0
OPERATING INCOME	80.1	92.7	192.1	663.7
Property and equipment, net	8,545.5	8,360.4	8,545.5	8,360.4
Jackups
Segment Reporting Information [Line Items]
Revenues	153.1	213.8	503.8	743.0
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	132.9	133.2	383.8	390.0
Depreciation	31.6	32.1	95.3	90.8
General and administrative	0.0	0.0	0.0	0.0
OPERATING INCOME	(11.4)	48.5	24.7	262.2
Property and equipment, net	2,502.4	2,537.9	2,502.4	2,537.9
Other
Segment Reporting Information [Line Items]
Revenues	15.2	15.1	44.3	60.5
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	13.8	11.2	40.3	48.4
Depreciation	0.0	0.0	0.0	0.0
General and administrative	0.0	0.0	0.0	0.0
OPERATING INCOME	1.4	3.9	4.0	12.1
Property and equipment, net	0.0	0.0	0.0	0.0
Operating Segments Total
Segment Reporting Information [Line Items]
Revenues	460.2	548.2	1,388.8	2,271.8
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	285.8	298.1	855.2	1,012.0
Depreciation	104.3	105.0	312.8	321.8
General and administrative	0.0	0.0	0.0	0.0
OPERATING INCOME	70.1	145.1	220.8	938.0
Property and equipment, net	11,047.9	10,898.3	11,047.9	10,898.3
Reconciling Items
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0	0.0
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	0.0	0.0	0.0	0.0
Depreciation	3.9	4.4	12.5	13.3
General and administrative	30.4	25.3	86.9	76.1
OPERATING INCOME	(34.3)	(29.7)	(99.4)	(89.4)
Property and equipment, net	$ 48.5	$ 61.4	$ 48.5	$ 61.4

The expense recognized in the current period that allocates the cost of a tangible asset used in providing revenue generating services over the asset's useful life.

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