Fair Values of Assets and Liabilities (Fair Value of Other Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Assets:
Held to maturity securities	$ 123,463	$ 120,373
Carrying Amount [Member]
Assets:
Cash and cash equivalents	13,096	11,490
Cash and investments segregated and on deposit for regulatory purposes	7,002	9,277
Receivables from brokers, dealers, and clearing organizations	894	649
Receivables from brokerage clients — net	21,144	20,568
Held to maturity securities	125,683	120,926
Bank loans – net	16,389	16,478
Other assets	656	781
Total	184,864	180,169
Liabilities:
Bank deposits	190,184	169,656
Payables to brokers, dealers, and clearing organizations	1,122	1,287
Payables to brokerage clients	31,088	31,243
Accrued expenses and other liabilities	1,173	1,463
Short-term borrowings		15,000
Long-term debt	4,128	4,753
Total	227,695	223,402
Carrying Amount [Member] | First Mortgage [Member]
Assets:
Bank loans – net	10,061	10,000
Carrying Amount [Member] | HELOCs [Member]
Assets:
Bank loans – net	1,789	1,935
Carrying Amount [Member] | Pledged asset lines [Member]
Assets:
Bank loans – net	4,362	4,369
Carrying Amount [Member] | Other [Member]
Assets:
Bank loans – net	177	174
Carrying Amount [Member] | U.S. agency mortgage-backed securities [Member]
Assets:
Held to maturity securities	103,967	101,197
Carrying Amount [Member] | Asset-backed securities [Member]
Assets:
Held to maturity securities	14,625	12,937
Carrying Amount [Member] | Corporate debt securities [Member]
Assets:
Held to maturity securities	4,340	4,078
Carrying Amount [Member] | U.S. state and municipal securities [Member]
Assets:
Held to maturity securities	1,245	1,247
Carrying Amount [Member] | Non-agency commercial mortgage-backed securities [Member]
Assets:
Held to maturity securities	1,033	994
Carrying Amount [Member] | Certificates of deposit [Member]
Assets:
Held to maturity securities	200	200
Carrying Amount [Member] | Foreign government agency securities [Member]
Assets:
Held to maturity securities	50	50
Carrying Amount [Member] | U.S. Treasury securities [Member]
Assets:
Held to maturity securities	223	223
Portion at Other than Fair Value Measurement [Member]
Assets:
Cash and cash equivalents	13,096	11,490
Cash and investments segregated and on deposit for regulatory purposes	7,002	9,277
Receivables from brokers, dealers, and clearing organizations	894	649
Receivables from brokerage clients — net	21,144	20,568
Held to maturity securities	123,463	120,373
Bank loans – net	16,238	16,485
Other assets	656	781
Total	182,493	179,623
Liabilities:
Bank deposits	190,184	169,656
Payables to brokers, dealers, and clearing organizations	1,122	1,287
Payables to brokerage clients	31,088	31,243
Accrued expenses and other liabilities	1,173	1,463
Short-term borrowings		15,000
Long-term debt	4,077	4,811
Total	227,644	223,460
Portion at Other than Fair Value Measurement [Member] | First Mortgage [Member]
Assets:
Bank loans – net	9,865	9,917
Portion at Other than Fair Value Measurement [Member] | HELOCs [Member]
Assets:
Bank loans – net	1,834	2,025
Portion at Other than Fair Value Measurement [Member] | Pledged asset lines [Member]
Assets:
Bank loans – net	4,362	4,369
Portion at Other than Fair Value Measurement [Member] | Other [Member]
Assets:
Bank loans – net	177	174
Portion at Other than Fair Value Measurement [Member] | U.S. agency mortgage-backed securities [Member]
Assets:
Held to maturity securities	101,672	100,453
Portion at Other than Fair Value Measurement [Member] | Asset-backed securities [Member]
Assets:
Held to maturity securities	14,744	13,062
Portion at Other than Fair Value Measurement [Member] | Corporate debt securities [Member]
Assets:
Held to maturity securities	4,304	4,086
Portion at Other than Fair Value Measurement [Member] | U.S. state and municipal securities [Member]
Assets:
Held to maturity securities	1,262	1,304
Portion at Other than Fair Value Measurement [Member] | Non-agency commercial mortgage-backed securities [Member]
Assets:
Held to maturity securities	1,017	999
Portion at Other than Fair Value Measurement [Member] | Certificates of deposit [Member]
Assets:
Held to maturity securities	200	200
Portion at Other than Fair Value Measurement [Member] | Foreign government agency securities [Member]
Assets:
Held to maturity securities	49	49
Portion at Other than Fair Value Measurement [Member] | U.S. Treasury securities [Member]
Assets:
Held to maturity securities	215	220
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Cash and cash equivalents	0	0
Cash and investments segregated and on deposit for regulatory purposes	0	0
Receivables from brokers, dealers, and clearing organizations	0	0
Receivables from brokerage clients — net	0	0
Held to maturity securities	0	0
Bank loans – net	0	0
Other assets	0	0
Total	0	0
Liabilities:
Bank deposits	0	0
Payables to brokers, dealers, and clearing organizations	0	0
Payables to brokerage clients	0	0
Accrued expenses and other liabilities	0	0
Short-term borrowings		0
Long-term debt	0	0
Total	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | First Mortgage [Member]
Assets:
Bank loans – net	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | HELOCs [Member]
Assets:
Bank loans – net	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Pledged asset lines [Member]
Assets:
Bank loans – net	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other [Member]
Assets:
Bank loans – net	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. agency mortgage-backed securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Asset-backed securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate debt securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. state and municipal securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Non-agency commercial mortgage-backed securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Certificates of deposit [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Foreign government agency securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Cash and cash equivalents	13,096	11,490
Cash and investments segregated and on deposit for regulatory purposes	7,002	9,277
Receivables from brokers, dealers, and clearing organizations	894	649
Receivables from brokerage clients — net	21,144	20,568
Held to maturity securities	123,463	120,373
Bank loans – net	16,238	16,485
Other assets	656	781
Total	182,493	179,623
Liabilities:
Bank deposits	190,184	169,656
Payables to brokers, dealers, and clearing organizations	1,122	1,287
Payables to brokerage clients	31,088	31,243
Accrued expenses and other liabilities	1,173	1,463
Short-term borrowings		15,000
Long-term debt	4,077	4,811
Total	227,644	223,460
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | First Mortgage [Member]
Assets:
Bank loans – net	9,865	9,917
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | HELOCs [Member]
Assets:
Bank loans – net	1,834	2,025
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pledged asset lines [Member]
Assets:
Bank loans – net	4,362	4,369
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other [Member]
Assets:
Bank loans – net	177	174
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. agency mortgage-backed securities [Member]
Assets:
Held to maturity securities	101,672	100,453
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Asset-backed securities [Member]
Assets:
Held to maturity securities	14,744	13,062
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate debt securities [Member]
Assets:
Held to maturity securities	4,304	4,086
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. state and municipal securities [Member]
Assets:
Held to maturity securities	1,262	1,304
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Non-agency commercial mortgage-backed securities [Member]
Assets:
Held to maturity securities	1,017	999
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Certificates of deposit [Member]
Assets:
Held to maturity securities	200	200
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign government agency securities [Member]
Assets:
Held to maturity securities	49	49
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury securities [Member]
Assets:
Held to maturity securities	215	220
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets:
Cash and cash equivalents	0	0
Cash and investments segregated and on deposit for regulatory purposes	0	0
Receivables from brokers, dealers, and clearing organizations	0	0
Receivables from brokerage clients — net	0	0
Held to maturity securities	0	0
Bank loans – net	0	0
Other assets	0	0
Total	0	0
Liabilities:
Bank deposits	0	0
Payables to brokers, dealers, and clearing organizations	0	0
Payables to brokerage clients	0	0
Accrued expenses and other liabilities	0	0
Short-term borrowings		0
Long-term debt	0	0
Total	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | First Mortgage [Member]
Assets:
Bank loans – net	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | HELOCs [Member]
Assets:
Bank loans – net	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Pledged asset lines [Member]
Assets:
Bank loans – net	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other [Member]
Assets:
Bank loans – net	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. agency mortgage-backed securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Asset-backed securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate debt securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. state and municipal securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Non-agency commercial mortgage-backed securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Certificates of deposit [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign government agency securities [Member]
Assets:
Held to maturity securities	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury securities [Member]
Assets:
Held to maturity securities	$ 0	$ 0