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Net Capital Requirements - Summary of Capital Adequacy Requirements (Detail) $ in Millions | Dec. 31, 2025 USD ($) | Dec. 31, 2024 USD ($)
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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

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