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, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	$ 497	$ 539
Available for sale securities	56,483	66,578
Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	521	522
Certificates of deposit [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	1,004	3,685
U.S. agency mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	40,431	25,556
U.S. Treasury securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	5,027	18,302
Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	4,801	10,085
Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	4,686	7,467
U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		898
Foreign government agency securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		49
Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	13	14
Fair Value, Recurring [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	5,116	8,292
Investments segregated and on deposit for regulatory purposes	3,556	4,671
Other securities owned	497	539
Available for sale securities	56,483	66,578
Total	65,652	80,080
Fair Value, Recurring [Member] | Money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	4,193	3,429
Fair Value, Recurring [Member] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	923	4,863
Available for sale securities	521	522
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	1,951	1,396
Available for sale securities	1,004	3,685
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	1,605	3,275
Fair Value, Recurring [Member] | Equity and bond mutual funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	378	441
Fair Value, Recurring [Member] | State and municipal debt obligations [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	32	39
Fair Value, Recurring [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	77	33
Fair Value, Recurring [Member] | Schwab Funds money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	10	26
Fair Value, Recurring [Member] | U.S. agency mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	40,431	25,556
Fair Value, Recurring [Member] | U.S. Treasury securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	5,027	18,302
Fair Value, Recurring [Member] | Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	4,801	10,085
Fair Value, Recurring [Member] | Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	4,686	7,467
Fair Value, Recurring [Member] | U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		898
Fair Value, Recurring [Member] | Foreign government agency securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		49
Fair Value, Recurring [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	13	14
Fair Value, Recurring [Member] | Level 1 [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	4,193	3,429
Investments segregated and on deposit for regulatory purposes	0	0
Other securities owned	391	470
Available for sale securities	0	0
Total	4,584	3,899
Fair Value, Recurring [Member] | Level 1 [Member] | Money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	4,193	3,429
Fair Value, Recurring [Member] | Level 1 [Member] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Available for sale securities	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
Available for sale securities	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
Fair Value, Recurring [Member] | Level 1 [Member] | Equity and bond mutual funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	378	441
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 securities owned	0	0
Fair Value, Recurring [Member] | 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	3	3
Fair Value, Recurring [Member] | Level 1 [Member] | Schwab Funds money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	10	26
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]
Available for sale securities	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]
Available for sale securities	0	0
Fair Value, Recurring [Member] | 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, Recurring [Member] | 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, Recurring [Member] | Level 1 [Member] | U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		0
Fair Value, Recurring [Member] | 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, Recurring [Member] | 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, Recurring [Member] | Level 2 [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	923	4,863
Investments segregated and on deposit for regulatory purposes	3,556	4,671
Other securities owned	106	69
Available for sale securities	56,483	66,578
Total	61,068	76,181
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	923	4,863
Available for sale securities	521	522
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	1,951	1,396
Available for sale securities	1,004	3,685
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	1,605	3,275
Fair Value, Recurring [Member] | 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, Recurring [Member] | Level 2 [Member] | State and municipal debt obligations [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	32	39
Fair Value, Recurring [Member] | 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	74	30
Fair Value, Recurring [Member] | 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, Recurring [Member] | 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	40,431	25,556
Fair Value, Recurring [Member] | Level 2 [Member] | U.S. Treasury securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	5,027	18,302
Fair Value, Recurring [Member] | Level 2 [Member] | Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	4,801	10,085
Fair Value, Recurring [Member] | Level 2 [Member] | Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	4,686	7,467
Fair Value, Recurring [Member] | Level 2 [Member] | U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		898
Fair Value, Recurring [Member] | Level 2 [Member] | Foreign government agency securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		49
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]
Available for sale securities	13	14
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
Other securities owned	0	0
Available for sale securities	0	0
Total	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	0
Available for sale securities	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
Available for sale securities	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
Fair Value, Recurring [Member] | 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, Recurring [Member] | 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, Recurring [Member] | 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, Recurring [Member] | 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, Recurring [Member] | 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, Recurring [Member] | 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, Recurring [Member] | 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, Recurring [Member] | 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, Recurring [Member] | Level 3 [Member] | U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		0
Fair Value, Recurring [Member] | Level 3 [Member] | Foreign government agency securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		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]
Available for sale securities	$ 0	$ 0