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, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	$ 500	$ 539
Available for sale securities	57,558	49,995
Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	2,540	2,727
Investments segregated and on deposit for regulatory purposes	1,950	5,856
Other securities owned	500	539
Available for sale securities	57,558	49,995
Total	62,548	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	552	2,727
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,988
Available for sale securities	518	313
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	1,950	2,198
Available for sale securities	2,769	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		3,658
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	394	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	21	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	44	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	41	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	23,955	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	12,243	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	9,387	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	6,922	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	1,682	1,906
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	34	40
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 1 [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	552	2,727
Investments segregated and on deposit for regulatory purposes	0	0
Other securities owned	418	455
Available for sale securities	0	0
Total	970	3,182
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 1 [Member] | Money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	552	2,727
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | 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] | 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] | 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
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 1 [Member] | Equity and bond mutual funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	394	318
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 1 [Member] | Schwab Funds money market funds [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	21	135
Fair Value, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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	2
Fair Value, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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	0
Fair Value, Measurements, Recurring [Member] | Fair Value [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	0
Fair Value, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [Member] | Level 2 [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,988	0
Investments segregated and on deposit for regulatory purposes	1,950	5,856
Other securities owned	82	84
Available for sale securities	57,558	49,995
Total	61,578	55,935
Fair Value, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [Member] | Level 2 [Member] | Commercial paper [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	1,988
Available for sale securities	518	313
Fair Value, Measurements, Recurring [Member] | Fair Value [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	1,950	2,198
Available for sale securities	2,769	2,041
Fair Value, Measurements, Recurring [Member] | Fair Value [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		3,658
Fair Value, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [Member] | Level 2 [Member] | State and municipal debt obligations [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Other securities owned	44	52
Fair Value, Measurements, Recurring [Member] | Fair Value [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	38	32
Fair Value, Measurements, Recurring [Member] | Fair Value [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	23,955	20,929
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 2 [Member] | U.S. Treasury securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	12,243	9,500
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 2 [Member] | Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	9,387	9,047
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 2 [Member] | Corporate debt securities [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	6,922	6,169
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Level 2 [Member] | U.S. agency notes [Member]
Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	1,682	1,906
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | 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] | 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	34	40
Fair Value, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [Member] | 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] | 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] | 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
Fair Value, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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, Measurements, Recurring [Member] | Fair Value [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	0
Fair Value, Measurements, Recurring [Member] | Fair Value [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	0
Fair Value, Measurements, Recurring [Member] | Fair Value [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