Fair Values of Assets and Liabilities - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | [1] | $ 107,646 | $ 147,871 |
U.S. agency mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 62,795 | 77,688 |
U.S. Treasury securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 21,471 | 40,002 |
Corporate debt securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 12,484 | 12,555 |
Asset-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 9,087 | 13,023 |
Foreign government agency securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 1,002 | 969 |
U.S. state and municipal securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 579 | 638 |
Non-agency commercial mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 109 | 450 |
Certificates of deposit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 100 | 2,231 |
Other | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 19 | 315 |
Fair Value, Recurring | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | 14,573 | 14,055 |
Total investments segregated and on deposit for regulatory purposes | | 20,358 | 24,645 |
Total available for sale securities | | 107,646 | 147,871 |
Total assets | | 1,913 | 1,432 |
Total assets | | 144,490 | 188,003 |
Total accrued expenses and other liabilities | | 1,733 | 1,261 |
Total liabilities | | 1,733 | 1,261 |
Fair Value, Recurring | Money market funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | 14,573 | 14,007 |
Fair Value, Recurring | Commercial paper | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | | 48 |
Fair Value, Recurring | U.S. Government securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total investments segregated and on deposit for regulatory purposes | | 20,358 | 23,645 |
Total assets | | 26 | 1 |
Fair Value, Recurring | U.S. agency mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 62,795 | 77,688 |
Fair Value, Recurring | U.S. Treasury securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 21,471 | 40,002 |
Fair Value, Recurring | Corporate debt securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 12,484 | 12,555 |
Fair Value, Recurring | Asset-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 9,087 | 13,023 |
Fair Value, Recurring | Foreign government agency securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 1,002 | 969 |
Fair Value, Recurring | U.S. state and municipal securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 579 | 638 |
Fair Value, Recurring | Non-agency commercial mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 109 | 450 |
Fair Value, Recurring | Certificates of deposit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total investments segregated and on deposit for regulatory purposes | | | 1,000 |
Total available for sale securities | | 100 | 2,231 |
Fair Value, Recurring | Other | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 19 | 315 |
Fair Value, Recurring | Total other securities owned | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 1,913 | 1,432 |
Fair Value, Recurring | Equity, corporate debt, and other securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 1,065 | 810 |
Fair Value, Recurring | Mutual funds and ETFs | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 795 | 596 |
Fair Value, Recurring | State and municipal debt obligations | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 27 | 25 |
Fair Value, Recurring | Other | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total accrued expenses and other liabilities | | 1,733 | 1,261 |
Fair Value, Recurring | Level 1 | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | 14,573 | 14,007 |
Total investments segregated and on deposit for regulatory purposes | | 0 | 0 |
Total available for sale securities | | 0 | 0 |
Total assets | | 1,787 | 1,351 |
Total assets | | 16,360 | 15,358 |
Total accrued expenses and other liabilities | | 1,644 | 1,218 |
Total liabilities | | 1,644 | 1,218 |
Fair Value, Recurring | Level 1 | Money market funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | 14,573 | 14,007 |
Fair Value, Recurring | Level 1 | Commercial paper | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | | 0 |
Fair Value, Recurring | Level 1 | U.S. Government securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total investments segregated and on deposit for regulatory purposes | | 0 | 0 |
Total assets | | 0 | 0 |
Fair Value, Recurring | Level 1 | U.S. agency mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 1 | U.S. Treasury securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 1 | Corporate debt securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 1 | Asset-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 1 | Foreign government agency securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 1 | U.S. state and municipal securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 1 | Non-agency commercial mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 1 | Certificates of deposit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total investments segregated and on deposit for regulatory purposes | | | 0 |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 1 | Other | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 1 | Total other securities owned | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 1,787 | 1,351 |
Fair Value, Recurring | Level 1 | Equity, corporate debt, and other securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 992 | 755 |
Fair Value, Recurring | Level 1 | Mutual funds and ETFs | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 795 | 596 |
Fair Value, Recurring | Level 1 | State and municipal debt obligations | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 0 | 0 |
Fair Value, Recurring | Level 1 | Other | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total accrued expenses and other liabilities | | 1,644 | 1,218 |
Fair Value, Recurring | Level 2 | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | 0 | 48 |
Total investments segregated and on deposit for regulatory purposes | | 20,358 | 24,645 |
Total available for sale securities | | 107,646 | 147,871 |
Total assets | | 126 | 81 |
Total assets | | 128,130 | 172,645 |
Total accrued expenses and other liabilities | | 89 | 43 |
Total liabilities | | 89 | 43 |
Fair Value, Recurring | Level 2 | Money market funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | 0 | 0 |
Fair Value, Recurring | Level 2 | Commercial paper | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | | 48 |
Fair Value, Recurring | Level 2 | U.S. Government securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total investments segregated and on deposit for regulatory purposes | | 20,358 | 23,645 |
Total assets | | 26 | 1 |
Fair Value, Recurring | Level 2 | U.S. agency mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 62,795 | 77,688 |
Fair Value, Recurring | Level 2 | U.S. Treasury securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 21,471 | 40,002 |
Fair Value, Recurring | Level 2 | Corporate debt securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 12,484 | 12,555 |
Fair Value, Recurring | Level 2 | Asset-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 9,087 | 13,023 |
Fair Value, Recurring | Level 2 | Foreign government agency securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 1,002 | 969 |
Fair Value, Recurring | Level 2 | U.S. state and municipal securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 579 | 638 |
Fair Value, Recurring | Level 2 | Non-agency commercial mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 109 | 450 |
Fair Value, Recurring | Level 2 | Certificates of deposit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total investments segregated and on deposit for regulatory purposes | | | 1,000 |
Total available for sale securities | | 100 | 2,231 |
Fair Value, Recurring | Level 2 | Other | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 19 | 315 |
Fair Value, Recurring | Level 2 | Total other securities owned | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 126 | 81 |
Fair Value, Recurring | Level 2 | Equity, corporate debt, and other securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 73 | 55 |
Fair Value, Recurring | Level 2 | Mutual funds and ETFs | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 0 | 0 |
Fair Value, Recurring | Level 2 | State and municipal debt obligations | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 27 | 25 |
Fair Value, Recurring | Level 2 | Other | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total accrued expenses and other liabilities | | 89 | 43 |
Fair Value, Recurring | Level 3 | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | 0 | 0 |
Total investments segregated and on deposit for regulatory purposes | | 0 | 0 |
Total available for sale securities | | 0 | 0 |
Total assets | | 0 | 0 |
Total assets | | 0 | 0 |
Total accrued expenses and other liabilities | | 0 | 0 |
Total liabilities | | 0 | 0 |
Fair Value, Recurring | Level 3 | Money market funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | 0 | 0 |
Fair Value, Recurring | Level 3 | Commercial paper | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total cash equivalents | | | 0 |
Fair Value, Recurring | Level 3 | U.S. Government securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total investments segregated and on deposit for regulatory purposes | | 0 | 0 |
Total assets | | 0 | 0 |
Fair Value, Recurring | Level 3 | U.S. agency mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 3 | U.S. Treasury securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 3 | Corporate debt securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 3 | Asset-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 3 | Foreign government agency securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 3 | U.S. state and municipal securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 3 | Non-agency commercial mortgage-backed securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 3 | Certificates of deposit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total investments segregated and on deposit for regulatory purposes | | | 0 |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 3 | Other | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total available for sale securities | | 0 | 0 |
Fair Value, Recurring | Level 3 | Total other securities owned | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 0 | 0 |
Fair Value, Recurring | Level 3 | Equity, corporate debt, and other securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 0 | 0 |
Fair Value, Recurring | Level 3 | Mutual funds and ETFs | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 0 | 0 |
Fair Value, Recurring | Level 3 | State and municipal debt obligations | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total assets | | 0 | 0 |
Fair Value, Recurring | Level 3 | Other | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total accrued expenses and other liabilities | | $ 0 | $ 0 |
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[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information. | |