Fair Values of Assets and Liabilities (Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions | Mar. 31, 2022 | Dec. 31, 2021 |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | $ 272,049 | $ 390,054 |
Commercial paper [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 200 | 200 |
Certificates of deposit [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,296 | 999 |
U.S. agency mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 201,534 | 334,355 |
U.S. Treasury securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 31,833 | 21,282 |
Asset-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 18,423 | 17,546 |
Corporate debt securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 14,608 | 12,344 |
U.S. state and municipal securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,576 | 1,687 |
Non-agency commercial mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,161 | 1,190 |
Foreign government agency securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,096 | 425 |
Other [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 322 | 26 |
Fair Value, Recurring [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 19,699 | 11,719 |
Investments segregated and on deposit for regulatory purposes: | 36,056 | 36,699 |
Fair Value | 272,049 | 390,054 |
Other assets: | 1,538 | 1,584 |
Total assets | 329,342 | 440,056 |
Accrued expenses and other liabilities | 1,379 | 1,399 |
Total liabilities | 1,379 | 1,399 |
Fair Value, Recurring [Member] | Money market funds [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 15,112 | 11,719 |
Fair Value, Recurring [Member] | Commercial paper [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 4,587 | |
Fair Value | 200 | 200 |
Fair Value, Recurring [Member] | Certificates of deposit [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 349 | 350 |
Fair Value | 1,296 | 999 |
Fair Value, Recurring [Member] | U.S. Government securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 35,707 | 36,349 |
Other assets: | 4 | 3 |
Fair Value, Recurring [Member] | U.S. agency mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 201,534 | 334,355 |
Fair Value, Recurring [Member] | U.S. Treasury securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 31,833 | 21,282 |
Fair Value, Recurring [Member] | Asset-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 18,423 | 17,546 |
Fair Value, Recurring [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 14,608 | 12,344 |
Fair Value, Recurring [Member] | U.S. state and municipal securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,576 | 1,687 |
Fair Value, Recurring [Member] | Non-agency commercial mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,161 | 1,190 |
Fair Value, Recurring [Member] | Foreign government agency securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,096 | 425 |
Fair Value, Recurring [Member] | Other [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 322 | 26 |
Fair Value, Recurring [Member] | Equity, corporate debt, and other securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 924 | 913 |
Fair Value, Recurring [Member] | Mutual Funds And Exchange Traded Funds (ETFs) [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 603 | 636 |
Fair Value, Recurring [Member] | State and municipal debt obligations [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 7 | 32 |
Fair Value, Recurring [Member] | Level 1 [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 15,112 | 11,719 |
Investments segregated and on deposit for regulatory purposes: | 0 | 0 |
Fair Value | 0 | 0 |
Other assets: | 1,468 | 1,490 |
Total assets | 16,580 | 13,209 |
Accrued expenses and other liabilities | 1,331 | 1,354 |
Total liabilities | 1,331 | 1,354 |
Fair Value, Recurring [Member] | Level 1 [Member] | Money market funds [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 15,112 | 11,719 |
Fair Value, Recurring [Member] | Level 1 [Member] | Commercial paper [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | Certificates of deposit [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 0 | 0 |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | U.S. Government securities [Member] | | |
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 [Member] | Level 1 [Member] | U.S. agency mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | U.S. Treasury securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | Asset-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | U.S. state and municipal securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | Non-agency commercial mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | Foreign government agency securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | Other [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 1 [Member] | Equity, corporate debt, and other securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 865 | 854 |
Fair Value, Recurring [Member] | Level 1 [Member] | Mutual Funds And Exchange Traded Funds (ETFs) [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 603 | 636 |
Fair Value, Recurring [Member] | Level 1 [Member] | State and municipal debt obligations [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring [Member] | Level 2 [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 4,587 | 0 |
Investments segregated and on deposit for regulatory purposes: | 36,056 | 36,699 |
Fair Value | 272,049 | 390,054 |
Other assets: | 70 | 94 |
Total assets | 312,762 | 426,847 |
Accrued expenses and other liabilities | 48 | 45 |
Total liabilities | 48 | 45 |
Fair Value, Recurring [Member] | Level 2 [Member] | Money market funds [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Fair Value, Recurring [Member] | Level 2 [Member] | Commercial paper [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 4,587 | |
Fair Value | 200 | 200 |
Fair Value, Recurring [Member] | Level 2 [Member] | Certificates of deposit [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 349 | 350 |
Fair Value | 1,296 | 999 |
Fair Value, Recurring [Member] | Level 2 [Member] | U.S. Government securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 35,707 | 36,349 |
Other assets: | 4 | 3 |
Fair Value, Recurring [Member] | Level 2 [Member] | U.S. agency mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 201,534 | 334,355 |
Fair Value, Recurring [Member] | Level 2 [Member] | U.S. Treasury securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 31,833 | 21,282 |
Fair Value, Recurring [Member] | Level 2 [Member] | Asset-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 18,423 | 17,546 |
Fair Value, Recurring [Member] | Level 2 [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 14,608 | 12,344 |
Fair Value, Recurring [Member] | Level 2 [Member] | U.S. state and municipal securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,576 | 1,687 |
Fair Value, Recurring [Member] | Level 2 [Member] | Non-agency commercial mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,161 | 1,190 |
Fair Value, Recurring [Member] | Level 2 [Member] | Foreign government agency securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 1,096 | 425 |
Fair Value, Recurring [Member] | Level 2 [Member] | Other [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 322 | 26 |
Fair Value, Recurring [Member] | Level 2 [Member] | Equity, corporate debt, and other securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 59 | 59 |
Fair Value, Recurring [Member] | Level 2 [Member] | Mutual Funds And Exchange Traded Funds (ETFs) [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring [Member] | Level 2 [Member] | State and municipal debt obligations [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 7 | 32 |
Fair Value, Recurring [Member] | Level 3 [Member] | | |
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 |
Accrued expenses and other liabilities | 0 | 0 |
Total liabilities | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Money market funds [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Commercial paper [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Cash equivalents: | 0 | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Certificates of deposit [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments segregated and on deposit for regulatory purposes: | 0 | 0 |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | U.S. Government securities [Member] | | |
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 [Member] | Level 3 [Member] | U.S. agency mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | U.S. Treasury securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Asset-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Corporate debt securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | U.S. state and municipal securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Non-agency commercial mortgage-backed securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Foreign government agency securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Other [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Fair Value | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Equity, corporate debt, and other securities [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | Mutual Funds And Exchange Traded Funds (ETFs) [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | 0 | 0 |
Fair Value, Recurring [Member] | Level 3 [Member] | State and municipal debt obligations [Member] | | |
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Other assets: | $ 0 | $ 0 |