Description of Business, Basis of Presentation and Significant Accounting Policies (Basic and Diluted Net Loss Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Numerator:
Net loss attributable to Lions Gate Entertainment Corp. shareholders	$ (18.9)	$ (188.4)	$ (284.2)
Denominator:
Weighted average common shares outstanding (in shares)	220.5	217.9	213.7
Basic net loss per common share (in usd per share)	$ (0.09)	$ (0.86)	$ (1.33)
Diluted net loss per common share (in usd per share)	$ (0.09)	$ (0.86)	$ (1.33)
Antidilutive securities excluded from the calculation of diluted earnings per share due to net loss, amount	2.2	2.2	7.1