Segment Information (Schedule Of Segment Reporting Information) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 457.5	$ 909.6	$ 928.6	$ 1,723.6
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	291.3	350.2	569.4	713.9
Depreciation	107.9	112.4	217.1	225.7
General and administrative	30.5	27.4	56.5	50.8
OPERATING INCOME	27.8	419.6	85.6	733.2
Property and equipment, net	11,059.0	11,021.2	11,059.0	11,021.2	$ 10,919.3
Floaters [Member]
Segment Reporting Information [Line Items]
Revenues	264.0	636.4	548.8	1,149.0
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	145.6	208.6	292.0	419.9
Depreciation	72.0	77.8	144.8	158.1
General and administrative	0.0	0.0	0.0	0.0
OPERATING INCOME	46.4	350.0	112.0	571.0
Property and equipment, net	8,493.2	8,414.1	8,493.2	8,414.1
Jackup [Member]
Segment Reporting Information [Line Items]
Revenues	178.9	251.3	350.7	529.2
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	132.3	122.3	250.9	256.8
Depreciation	31.6	30.1	63.7	58.7
General and administrative	0.0	0.0	0.0	0.0
OPERATING INCOME	15.0	98.9	36.1	213.7
Property and equipment, net	2,515.3	2,543.0	2,515.3	2,543.0
Other [Member]
Segment Reporting Information [Line Items]
Revenues	14.6	21.9	29.1	45.4
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	13.4	19.3	26.5	37.2
Depreciation	0.0	0.0	0.0	0.0
General and administrative	0.0	0.0	0.0	0.0
OPERATING INCOME	1.2	2.6	2.6	8.2
Property and equipment, net	0.0	0.0	0.0	0.0
Operating Segments Total [Member]
Segment Reporting Information [Line Items]
Revenues	457.5	909.6	928.6	1,723.6
Operating Expenses [Abstract]
Contract drilling (exclusive of depreciation)	291.3	350.2	569.4	713.9
Depreciation	103.6	107.9	208.5	216.8
General and administrative	0.0	0.0	0.0	0.0
OPERATING INCOME	62.6	451.5	150.7	792.9
Property and equipment, net	11,008.5	10,957.1	11,008.5	10,957.1
Reconciling Items [Member]
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	4.3	4.5	8.6	8.9
General and administrative	30.5	27.4	56.5	50.8
OPERATING INCOME	(34.8)	(31.9)	(65.1)	(59.7)
Property and equipment, net	$ 50.5	$ 64.1	$ 50.5	$ 64.1

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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