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, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	$ 500	$ 539
Available for sale securities	51,827	49,995
Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,049	2,727
Investments segregated and on deposit for regulatory purposes	5,808	5,856
Other securities owned	500	539
Available for sale securities	51,827	49,995
Total	59,184	59,117
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,049	2,727
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Certificates of deposit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Investments segregated and on deposit for regulatory purposes	2,147	2,198
Available for sale securities	1,791	2,041
Fair Value, Measurements, Recurring [Member] | Fair Value [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	3,661	3,658
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Equity and bond mutual funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	371	318
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Schwab Funds money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	59	135
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | State and municipal debt obligations [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	36	52
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Equity, U.S. Government and corporate debt, and other securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	34	34
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | U.S. agency mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	21,061	20,929
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | U.S. Treasury securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	10,827	9,500
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	9,636	9,047
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	6,552	6,169
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	1,557	1,906
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	315	313
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Foreign government agency securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	48	50
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	40	40
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,049	2,727
Investments segregated and on deposit for regulatory purposes	0	0
Other securities owned	432	455
Available for sale securities	0	0
Total	1,481	3,182
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,049	2,727
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (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
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (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
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity and bond mutual funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	371	318
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Schwab Funds money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	59	135
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | State and municipal debt obligations [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity, U.S. Government and corporate debt, and other securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	2	2
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. agency mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign government agency securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Investments segregated and on deposit for regulatory purposes	5,808	5,856
Other securities owned	68	84
Available for sale securities	51,827	49,995
Total	57,703	55,935
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (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	2,147	2,198
Available for sale securities	1,791	2,041
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (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	3,661	3,658
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Equity and bond mutual funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Schwab Funds money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | State and municipal debt obligations [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	36	52
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Equity, U.S. Government and corporate debt, and other securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	32	32
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. agency mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	21,061	20,929
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	10,827	9,500
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	9,636	9,047
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	6,552	6,169
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	1,557	1,906
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	315	313
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign government agency securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	48	50
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	40	40
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (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
Other securities owned	0	0
Available for sale securities	0	0
Total	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (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
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (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
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity and bond mutual funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Schwab Funds money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | State and municipal debt obligations [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity, U.S. Government and corporate debt, and other securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. agency mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign government agency securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Unobservable Inputs (Level 3) [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	$ 0	$ 0