Leases (Balance Sheet Information, Leases) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Mar. 31, 2020
Operating Leases
Operating leases, right-of-use assets	$ 134.3	$ 136.9
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Operating leases, lease liabilities (current)	$ 39.5	35.3
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrent
Operating leases, lease liabilities (non-current)	$ 130.2	129.6
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent
Operating leases, lease liabilities	$ 169.7	164.9
Finance Leases
Finance leases, right-of-use assets	$ 1.2	46.4
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	lgfa:PropertyPlantandEquipmentandFinanceLeaseRightofUseAssetafterAccumulatedDepreciationandAmortization
Finance leases, lease liabilities (current)	$ 1.0	3.0
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligationsCurrent
Finance leases, lease liabilities (non-current)	$ 0.0	39.4
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtAndCapitalLeaseObligations
Finance lease, lease liabilities	$ 1.0	$ 42.4
Operating leases, weighted average remaining lease term	5 years 6 months	6 years 1 month 6 days
Finance leases, weighted average remaining lease term	4 months 24 days	21 years 7 months 6 days
Operating leases, weighted average discount rate, percent	3.91%	4.10%
Finance leases, weighted average discount rate, percent	7.00%	6.40%