Contingencies (Narrative) (Details) shares in Millions, $ in Millions				1 Months Ended	3 Months Ended			6 Months Ended
		Nov. 08, 2018 USD ($)	Oct. 09, 2018 USD ($)	Aug. 30, 2016 class_action_complaint	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)	Mar. 16, 2017 plaintiff	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)	Nov. 05, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Shareholder litigation settlements	[1]				$ 114.1	$ 0.0		$ 114.1	$ 0.0
Dissenting shareholders' liability					$ 961.3			$ 961.3				$ 869.3
Petitions for appraisal filed | plaintiff							5
Starz Dissenting Shareholders | Starz
Loss Contingencies [Line Items]
Outstanding equity interests (in shares) | shares					22.5			22.5
Fiduciary Litigation
Loss Contingencies [Line Items]
Number of plaintiffs | class_action_complaint				7
Settlement payment amount					$ 92.5			$ 92.5
Insurance reimbursement receivable					37.8			37.8
Shareholder litigation settlements					54.8			54.8
Appraisal Litigation
Loss Contingencies [Line Items]
Settlement payment amount					961.0			961.0
Dissenting shareholders' liability before settlement amount					901.9			901.9
Shareholder litigation settlements					59.3			$ 59.3
Dissenting shareholders' liability											$ 885.2
Dissenting shareholders' liability, previously accrued interest											$ 87.9
Dissenting shareholders' liability, accrued interest for the quarter					$ 16.7
Subsequent Event | Fiduciary Litigation
Loss Contingencies [Line Items]
Settlement payment amount			$ 92.5
Lawsuit for insurance reimbursement, amount										$ 10.0
Subsequent Event | Appraisal Litigation
Loss Contingencies [Line Items]
Settlement payment amount		$ 961.0

[1] Shareholder litigation settlements of $114.1 million in the three and six months ended September 30, 2018 includes the following: (i) $54.8 million for the net expense recorded for the settlement of the Fiduciary Litigation (representing the settlement amount of $92.5 million, which the Company has included in accounts payable and accrued liabilities in the unaudited condensed consolidated balance sheet, net of aggregate insurance reimbursement of $37.8 million, which amount the Company has recorded a receivable included in the "other current assets" line item in the unaudited condensed consolidated balance sheet as of September 30, 2018) and (ii) $59.3 million related to the Appraisal Litigation, representing the amount by which the settlement amount of approximately $961 million exceeds the previously accrued $901.9 million dissenting shareholders' liability, before considering the settlement (i.e., dissenting shareholders' liability plus accrued interest through September 30, 2018). See Note 16.