Fair Values of Assets and Liabilities (Fair Value of Other Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets:
Fair Value	$ 120,373	$ 74,444
Reported Value Measurement [Member]
Assets:
Cash and cash equivalents	11,490	9,314
Cash and investments segregated and on deposit for regulatory purposes	9,277	13,533
Receivables from brokers, dealers, and clearing organizations	649	728
Receivables from brokerage clients — net	20,568	17,151
Fair Value	120,926	75,203
Bank loans, net	16,478	15,403
Other assets	781	328
Total	180,169	131,660
Liabilities:
Bank deposits	169,656	163,454
Payables to brokers, dealers, and clearing organizations	1,287	2,407
Payables to brokerage clients	31,243	35,894
Accrued expenses and other liabilities	1,463	1,169
Short-term borrowings	15,000
Long-term debt	4,753	2,876
Total	223,402	205,800
Reported Value Measurement [Member] | First Mortgage [Member]
Assets:
Bank loans, net	10,000	9,117
Reported Value Measurement [Member] | HELOC's [Member]
Assets:
Bank loans, net	1,935	2,342
Reported Value Measurement [Member] | Pledged asset lines [Member]
Assets:
Bank loans, net	4,369	3,851
Reported Value Measurement [Member] | Other [Member]
Assets:
Bank loans, net	174	93
Reported Value Measurement [Member] | U.S. agency mortgage-backed securities [Member]
Assets:
Fair Value	101,197	72,439
Reported Value Measurement [Member] | Non-agency commercial mortgage-backed securities [Member]
Assets:
Fair Value	994	997
Reported Value Measurement [Member] | Asset-backed securities [Member]
Assets:
Fair Value	12,937	941
Reported Value Measurement [Member] | Corporate debt securities [Member]
Assets:
Fair Value	4,078	436
Reported Value Measurement [Member] | U.S. Treasury securities [Member]
Assets:
Fair Value	223	223
Reported Value Measurement [Member] | Commercial paper [Member]
Assets:
Fair Value		99
Reported Value Measurement [Member] | U.S. state and municipal securities [Member]
Assets:
Fair Value	1,247	68
Reported Value Measurement [Member] | Certificates of deposit [Member]
Assets:
Fair Value	200
Reported Value Measurement [Member] | Foreign government agency securities [Member]
Assets:
Fair Value	50
Portion at Other than Fair Value Measurement [Member]
Assets:
Cash and cash equivalents	11,490	9,314
Cash and investments segregated and on deposit for regulatory purposes	9,277	13,533
Receivables from brokers, dealers, and clearing organizations	649	728
Receivables from brokerage clients — net	20,568	17,151
Fair Value	120,373	74,444
Bank loans, net	16,485	15,467
Other assets	781	328
Total	179,623	130,965
Liabilities:
Bank deposits	169,656	163,454
Payables to brokers, dealers, and clearing organizations	1,287	2,407
Payables to brokerage clients	31,243	35,894
Accrued expenses and other liabilities	1,463	1,169
Short-term borrowings	15,000
Long-term debt	4,811	2,941
Total	223,460	205,865
Portion at Other than Fair Value Measurement [Member] | First Mortgage [Member]
Assets:
Bank loans, net	9,917	9,064
Portion at Other than Fair Value Measurement [Member] | HELOC's [Member]
Assets:
Bank loans, net	2,025	2,458
Portion at Other than Fair Value Measurement [Member] | Pledged asset lines [Member]
Assets:
Bank loans, net	4,369	3,851
Portion at Other than Fair Value Measurement [Member] | Other [Member]
Assets:
Bank loans, net	174	94
Portion at Other than Fair Value Measurement [Member] | U.S. agency mortgage-backed securities [Member]
Assets:
Fair Value	100,453	71,677
Portion at Other than Fair Value Measurement [Member] | Non-agency commercial mortgage-backed securities [Member]
Assets:
Fair Value	999	1,004
Portion at Other than Fair Value Measurement [Member] | Asset-backed securities [Member]
Assets:
Fair Value	13,062	941
Portion at Other than Fair Value Measurement [Member] | Corporate debt securities [Member]
Assets:
Fair Value	4,086	436
Portion at Other than Fair Value Measurement [Member] | U.S. Treasury securities [Member]
Assets:
Fair Value	220	219
Portion at Other than Fair Value Measurement [Member] | Commercial paper [Member]
Assets:
Fair Value		99
Portion at Other than Fair Value Measurement [Member] | U.S. state and municipal securities [Member]
Assets:
Fair Value	1,304	68
Portion at Other than Fair Value Measurement [Member] | Certificates of deposit [Member]
Assets:
Fair Value	200
Portion at Other than Fair Value Measurement [Member] | Foreign government agency securities [Member]
Assets:
Fair Value	49
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
Fair Value	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] | HELOC's [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:
Fair Value	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:
Fair Value	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:
Fair Value	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:
Fair Value	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:
Fair Value	0	0
Portion at Other than Fair Value Measurement [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Commercial paper [Member]
Assets:
Fair Value		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:
Fair Value	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:
Fair Value	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:
Fair Value	0
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets:
Cash and cash equivalents	11,490	9,314
Cash and investments segregated and on deposit for regulatory purposes	9,277	13,533
Receivables from brokers, dealers, and clearing organizations	649	728
Receivables from brokerage clients — net	20,568	17,151
Fair Value	120,373	74,444
Bank loans, net	16,485	15,467
Other assets	781	328
Total	179,623	130,965
Liabilities:
Bank deposits	169,656	163,454
Payables to brokers, dealers, and clearing organizations	1,287	2,407
Payables to brokerage clients	31,243	35,894
Accrued expenses and other liabilities	1,463	1,169
Short-term borrowings	15,000
Long-term debt	4,811	2,941
Total	223,460	205,865
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | First Mortgage [Member]
Assets:
Bank loans, net	9,917	9,064
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | HELOC's [Member]
Assets:
Bank loans, net	2,025	2,458
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Pledged asset lines [Member]
Assets:
Bank loans, net	4,369	3,851
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other [Member]
Assets:
Bank loans, net	174	94
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. agency mortgage-backed securities [Member]
Assets:
Fair Value	100,453	71,677
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Non-agency commercial mortgage-backed securities [Member]
Assets:
Fair Value	999	1,004
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Asset-backed securities [Member]
Assets:
Fair Value	13,062	941
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate debt securities [Member]
Assets:
Fair Value	4,086	436
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury securities [Member]
Assets:
Fair Value	220	219
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Commercial paper [Member]
Assets:
Fair Value		99
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. state and municipal securities [Member]
Assets:
Fair Value	1,304	68
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Certificates of deposit [Member]
Assets:
Fair Value	200
Portion at Other than Fair Value Measurement [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign government agency securities [Member]
Assets:
Fair Value	49
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
Fair Value	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] | HELOC's [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:
Fair Value	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Non-agency commercial mortgage-backed securities [Member]
Assets:
Fair Value	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Asset-backed securities [Member]
Assets:
Fair Value	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate debt securities [Member]
Assets:
Fair Value	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury securities [Member]
Assets:
Fair Value	0	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Commercial paper [Member]
Assets:
Fair Value		0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. state and municipal securities [Member]
Assets:
Fair Value	0	$ 0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Certificates of deposit [Member]
Assets:
Fair Value	0
Portion at Other than Fair Value Measurement [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign government agency securities [Member]
Assets:
Fair Value	$ 0