Regulation and Capital Adequacy - Risk-Based Capital Ratios (Detail) - Group Inc. $ in Millions	Mar. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)
Standardized
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 capital	$ 101,800	$ 104,297
Tier 1 capital	115,189	118,943
Tier 2 capital	14,256	11,722
Total capital	129,445	130,665
RWAs	$ 815,106	$ 727,338
CET1 capital ratio	0.125	0.143
Tier 1 capital ratio	0.141	0.164
Total capital ratio	0.159	0.180
Advanced
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 capital	$ 101,800	$ 104,297
Tier 1 capital	115,189	118,943
Tier 2 capital	11,683	9,527
Total capital	126,872	128,470
RWAs	$ 763,768	$ 691,470
CET1 capital ratio	0.133	0.151
Tier 1 capital ratio	0.151	0.172
Total capital ratio	0.166	0.186

Amount of total capital as defined by regulatory framework.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477270/942-505-50-1

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Amount of Tier 2 risk-based capital as defined by regulatory framework.

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