Consolidated Lease Liabilities And Right-Of-Use Lease Assets Related To Operating Leases (Detail) $ in Millions	Dec. 31, 2021 USD ($)
Maturity of lease payments, by year
1 year or less	$ 50.3
More than 1 year to 2 years	45.7
More than 2 years to 3 years	42.7
More than 3 years to 4 years	35.4
More than 4 years to 5 years	30.3
More than 5 years	143.3
Total lease payments	347.7	[1]
Less: interest	(79.2)	[2]
Lease liabilities	$ 268.5	[3]
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesMember
Right-of-use lease assets	$ 240.5	[4]
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Assets
Prepaid lease assets, net of lease allowances and incentives	$ 28.0
Right-of-use lease assets and prepaid lease assets, net of lease allowances and incentives	$ 268.5

[1] As of December 31, 2021, the weighted average lease term was approximately 13 years.

[2] As of December 31, 2021, the weighted average discount rate was approximately 5 percent.

[3] Represents the present value of expected lease payments over the remaining lease term and is reported as a component of other liabilities on Alleghany’s consolidated balance sheet.

[4] Reported as a component of other assets on Alleghany’s consolidated balance sheet.