Capital Stock (Common Shares Reserved for Future Issuance) (Details) - shares shares in Millions	Dec. 31, 2017	Mar. 31, 2017
Common Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	48.0	50.8
Stock Options and Equity-Settled SARs
Common Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	33.3	33.4
Restricted Stock and Restricted Share Units - Unvested
Common Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	2.6	2.7
Convertible Senior Subordinated Notes
Common Shares Reserved For Future Issuance [Line Items]
Coupon rate	1.25%
Convertible Senior Subordinated Notes | April 2013 Notes
Common Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	2.1	2.1
April 2013 Notes | Convertible Senior Subordinated Notes
Common Shares Reserved For Future Issuance [Line Items]
Coupon rate	1.25%
Lionsgate Plan | Common shares available for future issuance under plan
Common Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	10.0	0.8
Starz Plan | Common shares available for future issuance under plan
Common Shares Reserved For Future Issuance [Line Items]
Shares reserved for future issuance (in shares)	0.0	11.8