Fair Values of Assets and Liabilities - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions | Sep. 30, 2024 | Dec. 31, 2023 |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | $ 90,018 | $ 107,646 |
U.S. agency mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 56,280 | 62,795 |
U.S. Treasury securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 15,623 | 21,471 |
Corporate debt securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 10,246 | 12,484 |
Asset-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 6,630 | 9,087 |
Foreign government agency securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 523 | 1,002 |
U.S. state and municipal securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 585 | 579 |
Non-agency commercial mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 112 | 109 |
Certificates of deposit | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | | 100 |
Other | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 19 | 19 |
Fair Value, Recurring | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 14,694 | 14,573 |
Investments segregated and on deposit for regulatory purposes: | 17,569 | 20,358 |
Fair Value | 90,018 | 107,646 |
Other assets: | 2,439 | 1,913 |
Total assets | 124,720 | 144,490 |
Total accrued expenses and other liabilities | 2,120 | 1,733 |
Total liabilities | 2,120 | 1,733 |
Fair Value, Recurring | Money market funds | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 14,694 | 14,573 |
Fair Value, Recurring | U.S. Government securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 17,569 | 20,358 |
Other assets: | 12 | 26 |
Fair Value, Recurring | U.S. agency mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 56,280 | 62,795 |
Fair Value, Recurring | U.S. Treasury securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 15,623 | 21,471 |
Fair Value, Recurring | Corporate debt securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 10,246 | 12,484 |
Fair Value, Recurring | Asset-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 6,630 | 9,087 |
Fair Value, Recurring | Foreign government agency securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 523 | 1,002 |
Fair Value, Recurring | U.S. state and municipal securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 585 | 579 |
Fair Value, Recurring | Non-agency commercial mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 112 | 109 |
Fair Value, Recurring | Certificates of deposit | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | | 100 |
Fair Value, Recurring | Other | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 19 | 19 |
Fair Value, Recurring | Total other securities owned | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 2,438 | 1,913 |
Fair Value, Recurring | Equity, corporate debt, and other securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 1,403 | 1,065 |
Fair Value, Recurring | Mutual funds and ETFs | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 981 | 795 |
Fair Value, Recurring | State and municipal debt obligations | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 42 | 27 |
Fair Value, Recurring | Interest rate swaps | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 1 | |
Fair Value, Recurring | Other | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total accrued expenses and other liabilities | 2,120 | 1,733 |
Fair Value, Recurring | Level 1 | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 14,694 | 14,573 |
Investments segregated and on deposit for regulatory purposes: | 0 | 0 |
Fair Value | 0 | 0 |
Other assets: | 2,299 | 1,787 |
Total assets | 16,993 | 16,360 |
Total accrued expenses and other liabilities | 2,084 | 1,644 |
Total liabilities | 2,084 | 1,644 |
Fair Value, Recurring | Level 1 | Money market funds | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 14,694 | 14,573 |
Fair Value, Recurring | Level 1 | U.S. Government securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 0 | 0 |
Other assets: | 0 | 0 |
Fair Value, Recurring | Level 1 | U.S. agency mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 1 | U.S. Treasury securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 1 | Corporate debt securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 1 | Asset-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 1 | Foreign government agency securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 1 | U.S. state and municipal securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 1 | Non-agency commercial mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 1 | Certificates of deposit | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | | 0 |
Fair Value, Recurring | Level 1 | Other | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 1 | Total other securities owned | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 2,299 | 1,787 |
Fair Value, Recurring | Level 1 | Equity, corporate debt, and other securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 1,318 | 992 |
Fair Value, Recurring | Level 1 | Mutual funds and ETFs | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 981 | 795 |
Fair Value, Recurring | Level 1 | State and municipal debt obligations | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring | Level 1 | Interest rate swaps | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | |
Fair Value, Recurring | Level 1 | Other | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total accrued expenses and other liabilities | 2,084 | 1,644 |
Fair Value, Recurring | Level 2 | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Investments segregated and on deposit for regulatory purposes: | 17,569 | 20,358 |
Fair Value | 90,018 | 107,646 |
Other assets: | 140 | 126 |
Total assets | 107,727 | 128,130 |
Total accrued expenses and other liabilities | 36 | 89 |
Total liabilities | 36 | 89 |
Fair Value, Recurring | Level 2 | Money market funds | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Fair Value, Recurring | Level 2 | U.S. Government securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 17,569 | 20,358 |
Other assets: | 12 | 26 |
Fair Value, Recurring | Level 2 | U.S. agency mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 56,280 | 62,795 |
Fair Value, Recurring | Level 2 | U.S. Treasury securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 15,623 | 21,471 |
Fair Value, Recurring | Level 2 | Corporate debt securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 10,246 | 12,484 |
Fair Value, Recurring | Level 2 | Asset-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 6,630 | 9,087 |
Fair Value, Recurring | Level 2 | Foreign government agency securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 523 | 1,002 |
Fair Value, Recurring | Level 2 | U.S. state and municipal securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 585 | 579 |
Fair Value, Recurring | Level 2 | Non-agency commercial mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 112 | 109 |
Fair Value, Recurring | Level 2 | Certificates of deposit | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | | 100 |
Fair Value, Recurring | Level 2 | Other | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 19 | 19 |
Fair Value, Recurring | Level 2 | Total other securities owned | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 139 | 126 |
Fair Value, Recurring | Level 2 | Equity, corporate debt, and other securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 85 | 73 |
Fair Value, Recurring | Level 2 | Mutual funds and ETFs | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring | Level 2 | State and municipal debt obligations | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 42 | 27 |
Fair Value, Recurring | Level 2 | Interest rate swaps | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 1 | |
Fair Value, Recurring | Level 2 | Other | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total accrued expenses and other liabilities | 36 | 89 |
Fair Value, Recurring | Level 3 | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Investments segregated and on deposit for regulatory purposes: | 0 | 0 |
Fair Value | 0 | 0 |
Other 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 Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Fair Value, Recurring | Level 3 | U.S. Government securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 0 | 0 |
Other assets: | 0 | 0 |
Fair Value, Recurring | Level 3 | U.S. agency mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 3 | U.S. Treasury securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 3 | Corporate debt securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 3 | Asset-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 3 | Foreign government agency securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 3 | U.S. state and municipal securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 3 | Non-agency commercial mortgage-backed securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 3 | Certificates of deposit | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | | 0 |
Fair Value, Recurring | Level 3 | Other | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring | Level 3 | Total other securities owned | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring | Level 3 | Equity, corporate debt, and other securities | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring | Level 3 | Mutual funds and ETFs | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring | Level 3 | State and municipal debt obligations | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring | Level 3 | Interest rate swaps | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | |
Fair Value, Recurring | Level 3 | Other | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total accrued expenses and other liabilities | $ 0 | $ 0 |