Net Capital Requirements - Summary of Capital Adequacy Requirements (Detail) $ in Millions	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Broker-Dealer, Net Capital Requirement, SEC Regulation [Abstract]
Total capital (to risk weighted assets), Actual, Amount	$ 851	$ 961
Total capital (to risk weighted assets), Actual, Ratio	0.1146	0.1532
Total capital (to risk weighted assets), For Capital Adequacy Purposes, Amount	$ 59	$ 50
Total capital (to risk weighted assets), For Capital Adequacy Purposes, Ratio	0.08	0.08
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 74	$ 63
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.10	0.10
Common Equity Tier 1 capital (to risk weighted assets), Actual, Amount	$ 846	$ 953
Common Equity Tier 1 capital (to risk weighted assets), Actual, Ratio	114.00%	151.90%
Common Equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes, Amount	$ 33	$ 28
Common Equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes, Ratio	4.50%	4.50%
Common Equity Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 48	$ 41
Common Equity Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	6.50%
Tier 1 capital (to risk weighted assets), Actual, Amount	$ 846	$ 953
Tier 1 capital (to risk weighted assets), Actual, Ratio	0.114	0.1519
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes, Amount	$ 45	$ 38
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes, Ratio	0.06	0.06
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 59	$ 50
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.08	0.08
Tier 1 capital (to average assets), Actual, Amount	$ 846	$ 953
Tier 1 capital (to average assets), Actual, Ratio	0.676	0.713
Tier 1 capital (to average assets), For Capital Adequacy Purposes, Amount	$ 50	$ 53
Tier 1 capital (to average assets), For Capital Adequacy Purposes, Ratio	0.04	0.04
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 63	$ 67
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	0.05	0.05

Common equity tier one risk based capital.

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Amount of total capital as defined by regulatory framework.

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Amount of minimum total risk-based capital required for capital adequacy as defined by regulatory framework.

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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

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-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

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Amount of Tier 1 leverage capital as defined by regulatory framework.

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