Segment Information (Reconciliation Of Total Segment Profit To The Company's Income (Loss) Before Income Taxes) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Company’s total segment profit									$ 561.9	$ 624.6	$ 714.0
Adjusted depreciation and amortization									(41.8)	(41.1)	(39.3)
Restructuring and other									(24.3)	(78.0)	(59.8)
COVID-19 related costs included in direct operating expense and distribution and marketing expense	$ (50.2)
Programming and content charges									(76.5)	(35.1)	0.0
Adjusted share-based compensation expense									(50.0)	(52.1)	(85.6)
Operating income	$ (12.0)	$ (39.5)	$ 57.6	$ (3.2)	$ (34.0)	$ 86.8	$ 39.1	$ 38.2	2.8	130.0	248.7
Interest expense									(191.3)	(198.9)	(193.7)
Shareholder litigation settlements									0.0	(114.1)	0.0
Interest and other income									8.8	12.0	10.4
Other expense									(11.1)	(4.7)	0.0
Gain (loss) on extinguishment of debt									5.4	(1.9)	(35.7)
Gain (loss) on investments									(0.5)	(87.6)	171.8
Equity interests income (loss)									(17.2)	(42.9)	(52.8)
Income (loss) before income taxes									(203.1)	(308.1)	148.7
Operating segments
Segment Reporting Information [Line Items]
Company’s total segment profit									561.9	624.6	714.0
Corporate
Segment Reporting Information [Line Items]
Corporate general and administrative expenses									(99.7)	(104.2)	(110.3)
Corporate and reconciling items
Segment Reporting Information [Line Items]
Adjusted depreciation and amortization									(41.8)	(41.1)	(39.3)
Restructuring and other									(24.3)	(78.0)	(59.8)
COVID-19 related costs included in direct operating expense and distribution and marketing expense									(50.2)	0.0	0.0
Programming and content charges									(76.5)	(35.1)	0.0
Adjusted share-based compensation expense									(50.0)	(52.1)	(85.6)
Purchase accounting and related adjustments									$ (216.6)	$ (184.1)	$ (170.3)