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Regulatory Matters - Additional Information (Detail) $ in Billions	Jun. 30, 2021 USD ($)	Mar. 31, 2020
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Maximum Asset Value Required To Be Maintained Leverage Ratio	$ 10
Tier 1 capital ratio of risk-weighted assets	0.025
Covid 19[Member] | Throughout Two Thousand And Twenty [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Leverage ratio	0.08
Tier One Leverage Capital to Average Assets	0.08
Covid 19[Member] | Throughout Two Thousand And Twenty One [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Leverage ratio	0.085
Tier One Leverage Capital to Average Assets	0.085
Covid 19[Member] | From Two Thousand And Twenty Two Onwards [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Leverage ratio	0.09
Tier One Leverage Capital to Average Assets	0.09
Minimum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Leverage ratio		0.08
Tier One Leverage Capital to Average Assets		0.08
Maximum [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Leverage ratio		0.09
Tier One Leverage Capital to Average Assets		0.09

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Maximum Asset Value Required To Be Maintained Leverage Ratio.

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- Definition

Ratio of Tier 1 capital to average assets as defined by regulatory framework.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

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- Definition

Ratio of Tier 1 risk-based capital to risk-weighted assets as defined by regulatory framework.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 505
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117337116&loc=SL5958568-112826

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