Amounts Recorded on Balance Sheets Related to Cumulative Basis Adjustments for Fair Value Hedges (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Carrying amount of the hedged liabilities	$ 298.3	$ 310.8
Medium-term Notes
Derivative [Line Items]
Cumulative basis adjustment included in the carrying amount	$ (18.7)	$ (6.2)

Net fair value of all derivative instruments designated as fair value hedging instruments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=117331979&loc=d3e41228-113958

Name:	us-gaap_FairValueHedgesAtFairValueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant