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	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	$ 427	$ 449
Available for sale securities	48,062	77,365
Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,835	1,514
Investments segregated and on deposit for regulatory purposes	5,014	8,636
Other securities owned	427	449
Available for sale securities	48,062	77,365
Total	55,338	87,964
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	1,720	1,514
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	115
Available for sale securities	312	214
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	1,200	2,525
Available for sale securities	1,843	2,071
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	3,814	6,111
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	294	272
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	68	108
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	35	41
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	30	28
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	19,746	33,195
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	9,996	20,335
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	6,468	9,852
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	7,699	8,623
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	1,907	1,907
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | U.S. state and municipal securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		1,123
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	41	45
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	50
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	1,720	1,514
Investments segregated and on deposit for regulatory purposes	0	0
Other securities owned	366	382
Available for sale securities	0	0
Total	2,086	1,896
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	1,720	1,514
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]
Cash equivalents	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] | 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	294	272
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	68	108
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	4	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] | 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. 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] | 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] | U.S. state and municipal securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		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] | 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
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	115	0
Investments segregated and on deposit for regulatory purposes	5,014	8,636
Other securities owned	61	67
Available for sale securities	48,062	77,365
Total	53,252	86,068
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] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	115
Available for sale securities	312	214
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	1,200	2,525
Available for sale securities	1,843	2,071
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	3,814	6,111
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	35	41
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	26	26
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	19,746	33,195
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	9,996	20,335
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	6,468	9,852
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	7,699	8,623
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	1,907	1,907
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. state and municipal securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		1,123
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	41	45
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	50
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] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0
Available for sale securities	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] | 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. 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] | 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] | U.S. state and municipal securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		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
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