TD Ameritrade Holding 10-K 16 Nov 18 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Sep. 30, 2018	Nov. 01, 2018	Mar. 29, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	AMTD
Entity Registrant Name	TD AMERITRADE HOLDING CORP
Entity Central Index Key	1,173,431
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		562,369,568
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Shell Company	false
Entity Public Float			$ 33.3

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
ASSETS
Cash and cash equivalents	$ 2,690	$ 1,472
Cash and investments segregated and on deposit for regulatory purposes	3,185	10,446
Receivable from brokers, dealers and clearing organizations	1,374	1,334
Receivable from clients, net	22,616	17,151
Receivable from affiliates	151	137
Other receivables, net	304	174
Securities owned, at fair value	156	503
Investments available-for-sale, at fair value (including $98 million and $99 million of securities pledged as collateral for repurchase agreements at September 30, 2018 and 2017, respectively)	484	746
Property and equipment at cost, net	792	752
Goodwill	4,227	4,213
Acquired intangible assets, net	1,329	1,470
Other assets	212	229
Total assets	37,520	38,627
Liabilities:
Payable to brokers, dealers and clearing organizations	2,980	2,504
Payable to clients	22,884	25,107
Accounts payable and other liabilities	896	815
Payable to affiliates	45	109
Securities sold under agreements to repurchase	96	97
Long-term debt	2,439	2,555
Deferred income taxes	177	193
Total liabilities	29,517	31,380
Stockholders' equity:
Preferred stock, $0.01 par value, 100 million shares authorized; none issued	0	0
Common stock, $0.01 par value, one billion shares authorized; 670 million shares issued; 2018 — 563 million shares outstanding; 2017 — 567 million shares outstanding	7	7
Additional paid-in capital	3,379	3,369
Retained earnings	7,011	6,011
Treasury stock, common, at cost: 2018 — 107 million shares; 2017 — 103 million shares	(2,371)	(2,116)
Deferred compensation	4	1
Accumulated other comprehensive loss	(27)	(25)
Total stockholders' equity	8,003	7,247
Total liabilities and stockholders' equity	$ 37,520	$ 38,627

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Statement of Financial Position [Abstract]
Securities pledged as collateral for repurchase agreements	$ 98	$ 99
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	1,000,000,000	1,000,000,000
Common stock, shares issued	670,000,000	670,000,000
Common stock, shares outstanding	563,000,000	567,000,000
Treasury stock, shares	107,000,000	103,000,000

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Transaction-based revenues:
Commissions and transaction fees	$ 1,969	$ 1,384	$ 1,372
Asset-based revenues:
Bank deposit account fees	1,541	1,107	926
Net interest revenue	1,272	690	595
Investment product fees	557	423	374
Total asset-based revenues	3,370	2,220	1,895
Other revenues	113	72	60
Net revenues	5,452	3,676	3,327
Operating expenses:
Employee compensation and benefits	1,555	962	839
Clearing and execution costs	189	149	136
Communications	179	131	137
Occupancy and equipment costs	302	181	171
Depreciation and amortization	142	102	92
Amortization of acquired intangible assets	141	79	86
Professional services	303	260	178
Advertising	293	254	260
Other	350	92	110
Total operating expenses	3,454	2,210	2,009
Operating income	1,998	1,466	1,318
Other expense:
Interest on borrowings	99	71	53
Loss on sale of investments	11	0	0
Other	1	1	0
Total other expense	111	72	53
Pre-tax income	1,887	1,394	1,265
Provision for income taxes	414	522	423
Net income	$ 1,473	$ 872	$ 842
Earnings per share - basic (in usd per share)	$ 2.60	$ 1.65	$ 1.59
Earnings per share - diluted (in usd per share)	$ 2.59	$ 1.64	$ 1.58
Weighted average shares outstanding - basic (in shares)	567	529	531
Weighted average shares outstanding - diluted (in shares)	569	531	534
Dividends declared per share (in usd per share)	$ 0.84	$ 0.72	$ 0.68

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 1,473	$ 872	$ 842
Investments available-for-sale:
Unrealized loss	(12)	(9)	0
Reclassification adjustment for realized loss included in net income	11	0	0
Net change in investments available-for-sale	(1)	(9)	0
Cash flow hedging instruments:
Reclassification adjustment for portion of realized loss amortized to net income	5	4	5
Total other comprehensive income (loss), before tax	4	(5)	5
Income tax effect	(2)	2	(2)
Total other comprehensive income (loss), net of tax	2	(3)	3
Comprehensive income	$ 1,475	$ 869	$ 845

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Deferred Compensation [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balance, value at Sep. 30, 2015	$ 4,903	$ 6	$ 1,649	$ 5,038	$ (1,765)	$ 0	$ (25)
Beginning balance (in shares) at Sep. 30, 2015		537
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	842			842
Other comprehensive income (loss), net of tax	3						3
Payment of cash dividends	(362)			(362)
Repurchases of common stock	(352)				(352)
Repurchases of common stock (in shares)		(12)
Repurchases of common stock for income tax withholding on stock-based compensation	(30)				(30)
Repurchase of common stock for income tax withholding on stock-based compensation (in shares)		(1)
Common stock issued for stock-based compensation, including tax effects	13		(13)		26
Common stock issued for stock-based compensation, including tax effects (in shares)		2
Stock-based compensation	34		34
Ending balance, value at Sep. 30, 2016	5,051	$ 6	1,670	5,518	(2,121)	0	(22)
Ending balance (in shares) at Sep. 30, 2016		526
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	872			872
Other comprehensive income (loss), net of tax	(3)						(3)
Payment of cash dividends	(379)			(379)
Issuance of common stock	400		400
Issuance of common stock (in shares)		11
Acquisition of Scottrade Financial Services, Inc.	1,262	$ 1	1,261
Acquisition of Scottrade Financial Services, Inc., (in shares)		28
Repurchases of common stock for income tax withholding on stock-based compensation	(27)				(27)
Repurchase of common stock for income tax withholding on stock-based compensation (in shares)		(1)
Common stock issued for stock-based compensation, including tax effects	34		2		32
Common stock issued for stock-based compensation, including tax effects (in shares)		3
Deferred compensation	1					1
Stock-based compensation	36		36
Ending balance, value at Sep. 30, 2017	$ 7,247	$ 7	3,369	6,011	(2,116)	1	(25)
Ending balance (in shares) at Sep. 30, 2017	567	567
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of Accounting Standards Update 2018-02 (Note 1)				4			(4)
Net income	$ 1,473			1,473
Other comprehensive income (loss), net of tax	2						2
Payment of cash dividends	(477)			(477)
Repurchases of common stock	(255)				(255)
Repurchases of common stock (in shares)		(5)
Future treasury stock purchases under accelerated stock repurchase agreement	(31)		(31)
Repurchases of common stock for income tax withholding on stock-based compensation	(17)				(17)
Common stock issued for stock-based compensation, including tax effects			(19)		19
Common stock issued for stock-based compensation, including tax effects (in shares)		1
Deferred compensation	1				(2)	3
Stock-based compensation	60		60
Ending balance, value at Sep. 30, 2018	$ 8,003	$ 7	$ 3,379	$ 7,011	$ (2,371)	$ 4	$ (27)
Ending balance (in shares) at Sep. 30, 2018	563	563

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 1,473	$ 872	$ 842
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	142	102	92
Amortization of acquired intangible assets	141	79	86
Deferred income taxes	(24)	(11)	(8)
Loss on sale of investments	11	0	0
Stock-based compensation	60	36	34
Provision for doubtful accounts on client and other receivables	69	6	5
Other, net	18	12	16
Changes in operating assets and liabilities:
Cash and investments segregated and on deposit for regulatory purposes	7,261	1,818	(2,424)
Receivable from brokers, dealers and clearing organizations	(40)	23	(328)
Receivable from clients, net	(5,536)	(2,079)	824
Receivable from/payable to affiliates, net	(79)	(5)	(11)
Other receivables, net	(129)	41	(16)
Securities owned, at fair value	347	(135)	94
Other assets	(39)	(5)	(17)
Payable to brokers, dealers and clearing organizations	476	110	(667)
Payable to clients	(2,223)	(196)	3,020
Accounts payable and other liabilities	(20)	31	(58)
Net cash provided by operating activities	1,908	699	1,484
Cash flows from investing activities:
Purchase of property and equipment	(229)	(197)	(105)
Proceeds from sale of property and equipment	12	0	0
Cash paid in business acquisition, net of cash and cash equivalents acquired	(4)	(1,288)	0
Purchase of short-term investments	(1)	(66)	(605)
Proceeds from sale and maturity of short-term investments	66	4	604
Purchase of investments available-for-sale, at fair value	(392)	0	(757)
Proceeds from sale of investments available-for-sale, at fair value	643	0	0
Purchase of other investments	(3)	0	0
Net cash provided by (used in) investing activities	92	(1,547)	(863)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	0	798	0
Payment of debt issuance costs	(3)	(8)	0
Principal payments on long-term debt	0	(385)	0
Reimbursement (payment) of prepayment premium on long-term debt	2
Reimbursement (payment) of prepayment premium on long-term debt		(54)	0
Proceeds from senior revolving credit facilities	3,225	0	0
Principal payments on senior revolving credit facilities	(3,225)	0	0
Net Proceeds from (payments on) securities sold under agreements to repurchase	(1)	97	0
Payment of cash dividends	(477)	(379)	(362)
Proceeds from issuance of common stock	0	400	0
Proceeds from exercise of stock options	0	23	0
Purchase of treasury stock	(255)	0	(352)
Purchase of treasury stock for income tax withholding on stock-based compensation	(17)	(27)	(30)
Payment for future treasury stock purchases under accelerated stock repurchase agreement	(31)	0	0
Net cash provided by (used in) financing activities	(782)	465	(744)
Net increase (decrease) in cash and cash equivalents	1,218	(383)	(123)
Cash and cash equivalents at beginning of year	1,472	1,855	1,978
Cash and cash equivalents at end of year	2,690	1,472	1,855
Supplemental cash flow information:
Interest paid	118	59	54
Income taxes paid	352	483	519
Noncash investing activities:
Issuance of common stock in acquisition	$ 0	$ 1,261	$ 0

Nature of Operations and Summar

Nature of Operations and Summary of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations and Summary of Significant Accounting Policies	Nature of Operations and Summary of Significant Accounting Policies Basis of Presentation — The consolidated financial statements include the accounts of TD Ameritrade Holding Corporation (the "Parent"), a Delaware corporation, and its wholly-owned subsidiaries (collectively, the "Company"). Intercompany balances and transactions have been eliminated. Nature of Operations — The Company provides securities brokerage services, including trade execution, clearing services and margin lending, through its broker-dealer subsidiaries; futures and foreign exchange trade execution services through its futures commission merchant ("FCM") and forex dealer member ("FDM") subsidiary; and trustee, custodial and other trust-related services to retirement plans and other custodial accounts through its state-chartered trust company subsidiary. The Company also provides cash sweep and deposit account products through third-party relationships, including relationships with affiliates. The Company's broker-dealer subsidiaries are subject to regulation by the Securities and Exchange Commission ("SEC"), the Financial Industry Regulatory Authority ("FINRA") and the various exchanges in which they maintain membership. The Company's FCM/FDM subsidiary is subject to regulation by the Commodity Futures Trading Commission ("CFTC") and the National Futures Association ("NFA"). Dividends from the Company's broker-dealer, FCM/FDM and trust company subsidiaries are a source of liquidity for the Parent. Requirements of the SEC, FINRA and CFTC relating to liquidity, net capital standards and the use of client funds and securities may limit funds available for the payment of dividends from the broker-dealer and FCM/FDM subsidiaries to the holding company. State regulatory requirements may limit funds available for the payment of dividends from the trust company subsidiary to the holding company. Use of Estimates — The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles ("GAAP") requires management to make estimates and assumptions that affect the reported amount of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Cash and Cash Equivalents — The Company considers temporary, highly-liquid investments with an original maturity of three months or less to be cash equivalents, except for amounts required to be segregated for regulatory purposes. Cash and Investments Segregated and on Deposit for Regulatory Purposes — Cash and investments segregated and on deposit for regulatory purposes consists primarily of qualified deposits in special reserve bank accounts for the exclusive benefit of clients under Rule 15c3-3 of the Securities Exchange Act of 1934 (the "Exchange Act") and other regulations. Funds can be held in cash, reverse repurchase agreements, U.S. Treasury securities, U.S. government agency mortgage-backed securities and other qualified securities. Reverse repurchase agreements (securities purchased under agreements to resell) are treated as collateralized financing transactions and are carried at amounts at which the securities will subsequently be resold, plus accrued interest. The Company's reverse repurchase agreements are collateralized by U.S. government debt securities and generally have a maturity of seven days. Cash and investments segregated and on deposit for regulatory purposes also includes amounts that have been segregated or secured for the benefit of futures clients according to the regulations of the CFTC governing futures commission merchants. Securities Borrowed and Securities Loaned — Securities borrowed and securities loaned transactions are recorded at the amount of cash collateral provided or received. Securities borrowed transactions require the Company to provide the counterparty with collateral in the form of cash. The Company receives collateral in the form of cash for securities loaned transactions. For these transactions, the fees earned or incurred by the Company are recorded as net interest revenue on the Consolidated Statements of Income. The related interest receivable from and the brokerage interest payable to broker-dealers are included in other receivables and in accounts payable and other liabilities, respectively, on the Consolidated Balance Sheets. Receivable from/Payable to Clients — Receivable from clients primarily consists of margin loans to securities brokerage clients, which are collateralized by client securities, and is carried at the amount receivable, net of an allowance for doubtful accounts that is primarily based on the amount of unsecured margin balances. Payable to clients primarily consists of client cash held in brokerage accounts and is carried at the amount of client cash on deposit. The Company earns interest revenue and pays interest expense on its receivable from client and payable to client balances, respectively. The interest revenue and expense are included in net interest revenue on the Consolidated Statements of Income. Securities Owned — Securities owned by our broker-dealer subsidiaries are recorded on a trade-date basis and carried at fair value, and the related changes in fair value are generally included in other revenues on the Consolidated Statements of Income. Investments Available-for-sale — Investments available-for-sale are carried at fair value and unrealized gains and losses, net of deferred income taxes, are reflected as a component of accumulated other comprehensive income (loss) on the Consolidated Balance Sheets. Realized gains and losses on investments available-for-sale are determined on the specific identification method and are reflected on the Consolidated Statements of Income. As of September 30, 2018 , investments available-for-sale consists of U.S. government debt securities with remaining contractual maturities between less than one year and six years. There were no material unrealized gains or losses on investments available-for-sale as of September 30, 2018 and 2017 . Property and Equipment — Property and equipment is recorded at cost, net of accumulated depreciation and amortization, except for land, which is recorded at cost. Depreciation is provided using the straight-line method over the estimated useful service lives of the assets, which range from seven to 40 years for buildings and building components and three to seven years for all other depreciable property and equipment. Leasehold improvements are amortized over the lesser of the economic useful life of the improvement or the term of the lease. Software Development — From the date technological feasibility has been established until beta testing is complete, software development costs are capitalized and included in property and equipment. Once the product is fully functional, such costs are amortized in accordance with the Company's normal accounting policies. Software development costs that do not meet capitalization criteria are expensed as incurred. Goodwill — The Company has recorded goodwill for purchase business combinations to the extent the purchase price of each completed acquisition exceeded the fair value of the net identifiable assets of the acquired company. The Company tests goodwill for impairment on an annual basis and more frequently as events occur or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. In performing the impairment tests, the Company utilizes quoted market prices of the Company's common stock to estimate the fair value of the Company as a whole. The estimated fair value is then allocated to the Company's reporting unit and is compared with the carrying value of the reporting unit. No impairment charges have resulted from the annual impairment tests. Amortization of Acquired Intangible Assets — Acquired intangible assets with finite lives are amortized on a straight-line basis over their estimated useful lives, ranging from two to 23 years. The acquired intangible asset associated with a trademark license agreement is not subject to amortization because the term of the agreement is considered to be indefinite. Long-Lived Assets and Acquired Intangible Assets — The Company reviews its long-lived assets and finite-lived acquired intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. If based on that review, changes in circumstances indicate that the carrying amount of such assets may not be recoverable, the Company evaluates recoverability by comparing the undiscounted cash flows associated with the asset to the asset's carrying amount. The Company also evaluates the remaining useful lives of intangible assets to determine if events or trends warrant a revision to the remaining period of amortization. Long-lived assets classified as "held for sale" are reported at the lesser of carrying amount or fair value less cost to sell. As of September 30, 2018 and 2017, the Company had $36 million and $5 million of assets classified as held for sale, respectively, which are included in other assets on the Consolidated Balance Sheets. The Company tests its indefinite-lived acquired intangible asset for impairment on an annual basis and more frequently as events occur or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. To determine if the indefinite-lived intangible asset is impaired, the Company first assesses certain qualitative factors. Based on this assessment, if it is determined that more likely than not the fair value of the indefinite-lived intangible asset is less than its carrying amount, the Company performs a quantitative impairment test. No impairment charges have resulted from the annual impairment tests. Securities Sold Under Agreements to Repurchase — Transactions involving sales of securities under agreements to repurchase (repurchase agreements) are treated as collateralized financing transactions. Under repurchase agreements, the Company receives cash from counterparties and provides U.S. Treasury securities as collateral. These agreements are carried at amounts at which the securities will subsequently be repurchased, plus accrued interest, and the interest expense incurred by the Company is recorded as interest on borrowings on the Consolidated Statements of Income. See " General Contingencies " in Note 15 , Commitments and Contingencies, for a discussion of the potential risks associated with repurchase agreements and how the Company mitigates those risks. Income Taxes — The Company files a consolidated U.S. income tax return with its subsidiaries on a calendar year basis, combined returns for state tax purposes where required and certain of its subsidiaries file separate state income tax returns where required. Deferred tax assets and liabilities are determined based on the differences between the financial statement carrying amounts and tax bases of assets and liabilities using enacted tax rates expected to apply to taxable income in the periods in which the deferred tax asset or liability is expected to be settled or realized. Uncertain tax positions are recognized if they are more likely than not to be sustained upon examination, based on the technical merits of the position. The amount of tax benefit recognized is the largest amount of benefit that is greater than 50% likely of being realized upon settlement. The Company recognizes interest and penalties, if any, related to income tax matters as part of the provision for income taxes on the Consolidated Statements of Income. Capital Stock — The authorized capital stock of the Company consists of a single class of common stock and one or more series of preferred stock as may be authorized for issuance by the Company's board of directors. Voting, dividend, conversion and liquidation rights of the preferred stock would be established by the board of directors upon issuance of such preferred stock. Stock-Based Compensation — The Company measures and recognizes compensation expense based on estimated grant date fair values for all stock-based payment arrangements. Stock-based compensation expense is based on awards expected to vest and therefore is reduced for estimated forfeitures. Forfeitures are estimated at the time of grant based on the Company's historical forfeiture experience and revised in subsequent periods if actual forfeitures differ from those estimates. Deferred Compensation — Company common stock held in a rabbi trust pursuant to a Company deferred compensation plan is recorded at the fair value of the stock at the time it is transferred to the rabbi trust and is classified as treasury stock. The corresponding deferred compensation liability is recorded as a component of stockholders' equity on the Consolidated Balance Sheets . Transaction-based Revenues — Client trades are recorded on a settlement-date basis with such trades generally settling within one to two business days after the trade date. Revenues and expenses related to client trades, including order routing revenue and revenues from markups on riskless principal trades in fixed-income securities, are recorded on a trade-date basis. Revenues related to client trades are recorded net of promotional allowances. Securities owned by clients, including those that collateralize margin or similar transactions, are not reflected in the accompanying consolidated financial statements. Bank Deposit Account Fees — Revenues generated from a sweep program that is offered to eligible clients of the Company whereby clients' uninvested cash is swept to FDIC-insured (up to specified limits) money market accounts at third-party financial institutions participating in the program. Bank deposit account fees includes revenues from the Insured Deposit Account ("IDA") agreement with TD Bank USA, N.A. ("TD Bank USA"), TD Bank, N.A. and The Toronto-Dominion Bank ("TD"). The IDA agreement is described further in Note 21 , Related Party Transactions. Net Interest Revenue — Net interest revenue primarily consists of income generated by interest charged to clients on margin balances, net interest revenue from securities borrowed and securities loaned transactions and interest earned on client cash, net of interest paid to clients on their credit balances. Investment Product Fees — Investment product fee revenue consists of revenues earned on client assets invested in money market mutual funds, other mutual funds and certain investment programs. Investment product fees also includes fees earned on client assets managed by independent registered investment advisors utilizing the Company's trading and investing platforms. Advertising — The Company expenses advertising costs the first time the advertising takes place. Client cash offers are also characterized as advertising expense, rather than as a reduction of revenue, because there is generally little or no cumulative revenue associated with an individual client earning a cash offer at the time the consideration is recognized in the Consolidated Statement of Income. Derivatives and Hedging Activities — The Company occasionally utilizes derivative instruments to manage risks, which may include market price, interest rate and foreign currency risks. The Company does not use derivative instruments for speculative or trading purposes. Derivatives are recorded on the Consolidated Balance Sheets as assets or liabilities at fair value. Derivative instruments properly designated to hedge exposure to changes in the fair value of assets or liabilities are accounted for as fair value hedges. Derivative instruments properly designated to hedge exposure to the variability of expected future cash flows or other forecasted transactions are accounted for as cash flow hedges. The Company formally documents the risk management objective and strategy for each hedge transaction. Derivative instruments that do not qualify for hedge accounting are carried at fair value on the Consolidated Balance Sheets with unrealized gains and losses recorded currently on the Consolidated Statements of Income. Cash flows from derivative instruments accounted for as fair value hedges or cash flow hedges are classified in the same category on the Consolidated Statements of Cash Flows as the cash flows from the items being hedged. For additional information on the Company's fair value and cash flow hedging instruments, see Note 10 , Long-term Debt and Other Borrowings. Earnings Per Share — Basic earnings per share ("EPS") is computed by dividing net income by the weighted average common shares outstanding for the period. Diluted EPS reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock, except when such assumed exercise or conversion would have an antidilutive effect on EPS. The difference between the numerator and denominator used in the Company's computation of basic and diluted earnings per share consists of common stock equivalent shares related to stock-based compensation. There were no material antidilutive awards for fiscal years 2018 and 2017. The Company excluded from the calculation of diluted earnings per share 0.4 million shares underlying the stock-based compensation awards for fiscal year 2016 because their inclusion would have been antidilutive. Recently Adopted Accounting Pronouncements ASU 2018-05 – In March 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2018-05, Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 . ASU 2018-05 amends Accounting Standards Codification ("ASC") 740, Income Taxes , to provide guidance on accounting for the tax effects of the Tax Cuts and Jobs Act (the "Act") pursuant to Staff Accounting Bulletin No. 118, which allows entities to complete the accounting under ASC 740 within a one-year measurement period from the Act's enactment date. This ASU was effective upon issuance. For additional information regarding the Company's accounting for the tax effects of the Act under this guidance, see Note 11, Income Taxes. ASU 2018-02 – In February 2018, the FASB issued ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income , to allow a reclassification from accumulated other comprehensive income (loss) to retained earnings for stranded income tax effects resulting from the Tax Cuts and Jobs Act enacted on December 22, 2017, and requires certain disclosures about stranded tax effects. The Company elected to early adopt the standard in the fourth quarter of fiscal year 2018, applying the updates in the period of adoption. As a result of the adoption, the Company reclassified $4 million of income tax benefits, related to cash flow hedging instruments, from accumulated other comprehensive loss to retained earnings on its Consolidated Balance Sheet. The reclassification related only to the change in the federal corporate income tax rate due to the Act. ASU 2016-09 – In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting . The guidance in ASU 2016-09 simplified several aspects of the accounting for share-based payment transactions, including: (1) recognize all excess tax benefits and tax deficiencies as income tax expense or benefit in the statement of income; (2) treat tax effects of exercised or vested awards as discrete items in the period in which they occur; (3) recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period; (4) classify excess tax benefits with other income tax cash flows as an operating activity; (5) an entity can make an accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur; (6) the threshold to qualify for equity classification will permit withholding up to the maximum statutory rates in the applicable jurisdictions; and (7) classify cash paid by an employer when directly withholding shares for tax withholding purposes as a financing activity in the statement of cash flows. The Company adopted the amended accounting guidance as of October 1, 2017, and as a result, the Company's provision for income taxes was reduced by $5 million on its Consolidated Statement of Income for the fiscal year ended September 30, 2018, due to the inclusion of excess tax benefits applied on a prospective basis. The future effects of excess tax benefits and tax deficiencies recognized in the Company's earnings will depend on the volume of equity compensation during a particular period and on the market price of the Company's common stock at the date the equity awards either vest or are exercised. In addition, the Company elected to retrospectively adopt the amendment to present excess tax benefits on share-based compensation as an operating activity on the statement of cash flows. This resulted in an increase in cash flows from operating activities and a decrease in cash flows from financing activities of $12 million and $16 million on the Company's Consolidated Statement of Cash Flows for the fiscal years ended September 30, 2017 and 2016, respectively. For the purpose of recognizing compensation cost associated with share-based awards, the Company has elected to continue to follow its current practice of estimating forfeitures. None of the other provisions in this amended guidance had a significant impact on the Company's consolidated financial statements. Recently Issued Accounting Pronouncements ASU 2018-13 – In August 2018, the FASB issued ASU 2018-13, Disclosure Framework–Changes to the Disclosure Requirements for Fair Value Measurement. The amendments in this standard will remove, modify and add certain disclosures under ASC Topic 820, Fair Value Measurement , with the objective of improving disclosure effectiveness. ASU 2018-13 will be effective for the Company's fiscal year beginning October 1, 2020, with early adoption permitted. The transition requirements are dependent upon each amendment within this update and will be applied either prospectively or retrospectively. Since this update is intended to modify disclosures, the adoption of ASU 2018-13 is not expected to have a material impact on the Company's consolidated financial statements. ASU 2017-12 – In August 2017, the FASB issued ASU 2017-12, Targeted Improvements to Accounting for Hedging Activities , which will amend the guidance in ASC Topic 815, Derivatives and Hedging. The objective of this ASU is to improve the financial reporting of hedging relationships to better portray the economic results of an entity's risk management activities in its financial statements through changes to both the designation and measurement guidance for qualifying hedging relationships and to the presentation of hedge results. In addition, the amendments in this ASU make certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP. All transition requirements and elections under ASU 2017-12 should be applied to hedging relationships existing on the date of adoption, with the effect of the adoption reflected as of the beginning of the fiscal year of adoption. The amended presentation and disclosure guidance is required only prospectively. ASU 2017-12 will be effective for the Company's fiscal year beginning October 1, 2019, with early adoption permitted. The Company is currently assessing the impact this ASU will have on its consolidated financial statements. ASU 2017-04 – In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment, which is intended to simplify the test for goodwill impairment by eliminating Step 2 from the goodwill impairment test, which measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. Under the amendments in this ASU, an entity should perform its annual goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. When measuring the goodwill impairment loss, income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit should be considered, if applicable. An entity will still have the option to perform the qualitative assessment for a reporting unit to determine if the quantitative test is necessary. ASU 2017-04 should be applied prospectively and will be effective for the Company's fiscal year beginning October 1, 2020, with early adoption permitted. The Company does not expect this ASU to have a material impact on its consolidated financial statements. ASU 2016-18 – In November 2016, the FASB issued ASU 2016-18, Restricted Cash . This ASU will amend the guidance in ASC Topic 230, Statement of Cash Flows , and is intended to reduce the diversity in the classification and presentation of changes in restricted cash on the statement of cash flows. The amendments within this ASU will require that the reconciliation of the beginning-of-period and end-of-period cash and cash equivalents amounts shown on the statement of cash flows include restricted cash and restricted cash equivalents. If restricted cash and restricted cash equivalents are presented separately from cash and cash equivalents on the balance sheet, an entity will be required to reconcile the amounts presented on the statement of cash flows to the amounts on the balance sheet. An entity will also be required to disclose information regarding the nature of the restrictions. ASU 2016-18 requires retrospective application and became effective for the Company's fiscal year beginning October 1, 2018. The adoption of ASU 2016-18 will change the manner in which restricted cash and restricted cash equivalents are presented in the Company's consolidated financial statements. ASU 2016-16 – In October 2016, the FASB issued ASU 2016-16, Intra-Entity Transfers of Assets Other Than Inventory. This ASU will amend the guidance in ASC Topic 740, Income Taxes . The amendments in this ASU are intended to improve the accounting for the income tax consequences of intra-entity transfers of assets other than inventory by requiring an entity to recognize the income tax consequences when a transfer occurs, instead of when the asset is sold to a third party. ASU 2016-16 requires modified retrospective adoption and became effective for the Company's fiscal year beginning October 1, 2018. The adoption of ASU 2016-16 did not have an impact on the Company's consolidated financial statements. ASU 2016-13 – In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments . The main objective of ASU 2016-13 is to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by an entity at each reporting date. To achieve this objective, the amendments in this update replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to develop credit loss estimates. ASU 2016-13 will be effective for the Company's fiscal year beginning October 1, 2020, using a modified retrospective approach. Early adoption is permitted. The Company is currently assessing the impact this ASU will have on its consolidated financial statements. ASU 2016-02 – In February 2016, the FASB issued ASU 2016-02, Leases . This ASU will supersede the guidance in ASC Topic 840, Leases . Under ASU 2016-02, for lease arrangements exceeding a 12-month term, a lessee will be required to recognize in the balance sheet a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. ASU 2016-02 will retain a distinction between finance and operating leases; however, the principal difference from the previous guidance is that lease assets and liabilities arising from operating leases will be recognized in the balance sheet. The recognition, measurement and presentation of expenses and cash flows arising from a lease by a lessee will not significantly change from current GAAP. The accounting applied by a lessor will be largely unchanged from that applied under current GAAP. Subsequent to issuing ASU 2016-02, the FASB has issued additional standards for the purpose of clarifying certain aspects of ASU 2016-02 and providing an additional (optional) transition method with which to adopt the new leases standard. The subsequently issued ASUs have the same effective date and transition requirements as ASU 2016-02. Under ASU 2016-02, an entity may apply the amendments by using one of the following two methods: (1) recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach or (2) apply the standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. ASU 2016-02 will be effective for the Company's fiscal year beginning October 1, 2019, with early adoption permitted. The Company has not selected a transition method and is currently assessing the impact of this ASU, but does not expect the standard to have a material impact on its net income. Upon adoption of ASU 2016-02, the Company expects to recognize right-of-use assets and lease liabilities for its operating leases, with initial measurement as defined by the ASU, in its Consolidated Balance Sheets. ASU 2014-09 – In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers , to clarify the principles of recognizing revenue from contracts with customers and to improve financial reporting by creating common revenue recognition guidance for U.S. GAAP and International Financial Reporting Standards. This ASU will supersede the revenue recognition requirements in ASC Topic 605, Revenue Recognition, and most industry-specific guidance. Entities are required to apply the following steps when recognizing revenue under ASU 2014-09: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when (or as) the entity satisfies a performance obligation. This ASU also requires additional disclosures related to the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. An entity may apply the amendments by using one of the following two methods: (1) retrospective application to each prior reporting period presented or (2) a modified retrospective approach, requiring the standard be applied only to the most current period presented, with the cumulative effect of initially applying the standard recognized at the date of initial application. ASU 2014-09 is effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period, with early adoption permitted. Subsequent to issuing ASU 2014-09, the FASB has issued additional standards for the purpose of clarifying certain aspects of ASU 2014-09. The subsequently issued ASUs have the same effective date and transition requirements as ASU 2014-09. The guidance does not apply to revenue associated with financial instruments, such as interest revenue, which is accounted for under other GAAP. Accordingly, net interest revenue will not be impacted. The Company adopted the revenue recognition standard as of October 1, 2018 using the modified retrospective method of adoption. This adoption did not have a material impact on the Company's financial condition, results of operations or cash flows as the satisfaction of performance obligations under the new guidance is materially consistent with the Company's previous revenue recognition policies. Similarly, the amended guidance did not have a material impact on the recognition of costs incurred to obtain new contracts with clients. The Company

Business Acquisition

Business Acquisition	12 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Business Acquisition	Business Acquisition On September 18, 2017 , the Company completed its acquisition of Scottrade Financial Services, Inc. ("Scottrade"), pursuant to an Agreement and Plan of Merger dated October 24, 2016 (the "Acquisition"), among the Company, Rodger O. Riney, as Voting Trustee of the Rodger O. Riney Family Voting Trust U/A/D 12/31/2012 (the "Riney Stockholder"), and Alto Acquisition Corp., a wholly-owned subsidiary of the Company. Founded in 1980, Scottrade provided securities brokerage and investment services to retail investors and traders, and independent registered investment advisors through its online platform as well as through nearly 500 branch locations. Immediately prior to the closing of the Acquisition, pursuant to the terms and conditions set forth in a separate Agreement and Plan of Merger, TD Bank, N.A., a wholly-owned subsidiary of The Toronto-Dominion Bank ("TD"), acquired Scottrade Bank, which was a wholly-owned subsidiary of Scottrade, from Scottrade (the "Bank Merger") for approximately $1.37 billion in cash (the "Bank Merger Consideration"). Immediately prior to the closing of the Acquisition, the Company also issued 11,074,197 shares of the Company's common stock to TD at a price of $36.12 per share, or approximately $400 million , pursuant to a subscription agreement dated October 24, 2016 between the Company and TD. Immediately following the Bank Merger, the Acquisition was completed. The aggregate consideration paid by the Company for all of the outstanding capital stock of Scottrade consisted of 27,685,493 shares of the Company's common stock and $3.07 billion in cash (the "Cash Consideration"). The Cash Consideration was funded with the Bank Merger Consideration paid by TD Bank, N.A. to Scottrade, the proceeds received from the Company's issuance of the 3.300% Senior Notes on April 27, 2017 , cash on hand and cash proceeds from the sale of the Company's common stock to TD, as described above. At the closing of the Acquisition, 1,736,815 shares of the Company's common stock otherwise payable to the Riney Stockholder were deposited into a third-party custodian account (the “Escrow Account”) pursuant to an escrow agreement to secure certain indemnification obligations of the Riney Stockholder. In connection with the closing of the Acquisition, the Company entered into a registration rights agreement with TD, the Riney Stockholder and the other stockholders described therein (the "Ricketts Stockholders") providing for certain customary registration rights with respect to their shares of the Company's common stock. Additionally, the Company and the Riney Stockholder entered into a stockholders agreement (the "Riney Stockholders Agreement"), which contained various provisions relating to stock ownership, voting, election of directors and other matters. On December 14, 2017, all of the Company's common stock received as consideration by the Riney Stockholder in the Acquisition, including shares held in the Escrow Account, were sold in a public offering. Prior to the public offering, the Riney Stockholder replaced the shares previously held in the Escrow Account with cash. As a result of the Riney Stockholder no longer owning any shares of the Company's common stock, the registration rights agreement was terminated solely with respect to the Riney Stockholder and the Riney Stockholders Agreement was terminated. The Company accounted for the purchase of Scottrade using the acquisition method of accounting under GAAP and accordingly, the purchase price of the Acquisition was allocated to the assets acquired and liabilities assumed based on their estimated fair values as of the date of acquisition. During the fiscal year ended September 30, 2018, the Company recorded purchase accounting adjustments, primarily attributable to post-closing adjustments related to the Bank Merger Consideration, assets acquired and liabilities assumed, resulting in a net increase in goodwill of $14 million . The purchase price allocation was finalized during September 2018, one-year from the anniversary of the Acquisition. Differences between purchase accounting estimates and actual results that arose prior to September 18, 2018 resulted in adjustments to the purchase price allocation. Any such adjustments arising on or after September 18, 2018 will be recorded in earnings. Goodwill associated with the Acquisition was primarily attributable to the anticipated synergies from combining the operations of the Company and Scottrade. Approximately $1.63 billion of the goodwill associated with the Acquisition is expected to be deductible for income tax purposes. The purchase price for Scottrade was comprised of the following (dollars in millions): TD Ameritrade Holding Corporation common stock issued to the Riney Stockholder and the Escrow Account (1) $ 1,261 Cash paid at closing (2) 3,073 Total purchase price $ 4,334 (1) Represents the value of 27,685,493 shares of the Company's common stock at a price of $45.55 per share. The per share value is based on the opening market price of the Company's common stock as of September 18, 2017, the Acquisition date. As discussed above, the shares held in the Escrow Account were sold and replaced with cash. (2) Includes $1.37 billion of Bank Merger Consideration paid by TD Bank, N.A. to Scottrade, which was used to fund a portion of the Acquisition. The purchase price allocation for Scottrade is summarized as follows (dollars in millions): Cash and cash equivalents (1) $ 1,785 Cash and investments segregated and on deposit for regulatory purposes 3,535 Receivable from brokers, dealers and clearing organizations 167 Receivable from clients, net 3,136 Receivable from affiliates 2 Other receivables 54 Securities owned 37 Property and equipment 136 Goodwill 1,760 Acquired intangible assets 974 Deferred tax assets 70 Other assets 35 Total assets acquired 11,691 Payable to brokers, dealers and clearing organizations (354 ) Payable to clients (6,248 ) Accounts payable and other liabilities (272 ) Payable to affiliates (47 ) Long-term debt (2) (436 ) Total liabilities assumed (7,357 ) Total provisional purchase price allocated $ 4,334 (1) Includes $1.37 billion of Bank Merger Consideration paid by TD Bank, N.A. to Scottrade, which was used to fund a portion of the Acquisition. (2) On the date of Acquisition, amounts owed by Scottrade under its 6.125% senior notes, including a prepayment premium, and the amount owed under its 6.18% secured loan were repaid by the Company. The results of operations for Scottrade are included in the Company's consolidated financial statements from the date of Acquisition. The following unaudited pro forma financial information sets forth the results of operations of the Company as if the Acquisition had occurred on October 1, 2015, the beginning of the comparable fiscal year prior to the year of Acquisition. The unaudited pro forma results include certain adjustments for acquisition-related costs, depreciation, amortization of intangible assets, interest expense on acquisition financing, and related income tax effects, and do not reflect potential revenue enhancements, cost savings or operating synergies that the Company expects to realize after the Acquisition. The unaudited pro forma financial information is based on currently available information, is presented for informational purposes only, and is not indicative of future operations or results had the Acquisition been completed as of October 1, 2015 or any other date. The following table summarizes the unaudited pro forma financial information for the fiscal years indicated (dollars in millions): 2017 2016 (unaudited) Pro forma net revenues $ 4,586 $ 4,158 Pro forma net income $ 921 $ 700 Pro forma basic earnings per share $ 1.62 $ 1.23 Pro forma diluted earnings per share $ 1.62 $ 1.22

Cash and Cash Equivalents

Cash and Cash Equivalents	12 Months Ended
	Sep. 30, 2018
Cash and Cash Equivalents [Abstract]
Cash and Cash Equivalents	Cash and Cash Equivalents The Company's cash and cash equivalents is summarized in the following table (dollars in millions): September 30, 2018 2017 Broker-dealer subsidiaries $ 2,094 $ 997 Corporate 342 279 Trust company subsidiary 124 79 Futures commission merchant and forex dealer member subsidiary 89 98 Investment advisory subsidiaries 41 19 Total $ 2,690 $ 1,472 Capital requirements may limit the amount of cash available for dividend from the broker-dealer, trust company and FCM/FDM subsidiaries to the Parent.

Cash and Investments Segregated

Cash and Investments Segregated and on Deposit for Regulatory Purposes	12 Months Ended
	Sep. 30, 2018
Restricted Cash and Investments [Abstract]
Cash and Investments Segregated and on Deposit for Regulatory Purposes	Cash and Investments Segregated and on Deposit for Regulatory Purposes Cash and investments segregated and on deposit for regulatory purposes consists of the following (dollars in millions): September 30, 2018 2017 U.S. government agency mortgage-backed securities $ 1,302 $ 1,486 Cash in demand deposit accounts 956 3,653 Reverse repurchase agreements (collateralized by U.S. government debt securities) 500 1,004 Cash on deposit with futures commission merchants 202 209 U.S. government debt securities 200 4,019 U.S. government debt securities on deposit with futures commission merchant 25 75 Total $ 3,185 $ 10,446

Receivable from and Payable to

Receivable from and Payable to Brokers, Dealers and Clearing Organizations	12 Months Ended
	Sep. 30, 2018
Brokers and Dealers [Abstract]
Receivable from and Payable to Brokers, Dealers and Clearing Organizations	Receivable from and Payable to Brokers, Dealers and Clearing Organizations Amounts receivable from and payable to brokers, dealers and clearing organizations consist of the following (dollars in millions): September 30, 2018 2017 Receivable: Deposits paid for securities borrowed $ 803 $ 1,154 Clearing organizations 545 151 Broker-dealers 14 21 Securities failed to deliver 12 8 Total $ 1,374 $ 1,334 Payable: Deposits received for securities loaned $ 2,914 $ 2,449 Securities failed to receive 34 21 Clearing organizations 29 32 Broker-dealers 3 2 Total $ 2,980 $ 2,504

Allowance for Doubtful Accounts

Allowance for Doubtful Accounts on Receivables	12 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Allowance for Doubtful Accounts on Receivables	Allowance for Doubtful Accounts on Receivables The following table summarizes activity in the Company's allowance for doubtful accounts on client and other receivables for the fiscal years indicated (dollars in millions): 2018 2017 2016 Beginning balance $ 11 $ 9 $ 12 Provision for doubtful accounts, net 56 2 2 Acquired in business acquisition — 2 — Write-off of doubtful accounts (13 ) (2 ) (5 ) Ending balance $ 54 $ 11 $ 9

Property and Equipment

Property and Equipment	12 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and Equipment Property and equipment consists of the following (dollars in millions): September 30, 2018 2017 Buildings and building components $ 462 $ 351 Computer equipment 326 270 Software 178 215 Leasehold improvements 176 173 Building construction in process — 101 Land 61 77 Other property and equipment 92 83 1,295 1,270 Less: Accumulated depreciation and amortization (503 ) (518 ) Property and equipment at cost, net $ 792 $ 752

Goodwill and Acquired Intangibl

Goodwill and Acquired Intangible Assets	12 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Acquired Intangible Assets	Goodwill and Acquired Intangible Assets The Company has recorded goodwill for business acquisitions to the extent the purchase price of each completed acquisition exceeded the fair value of the net identifiable tangible and intangible assets of each acquired company. The following table summarizes changes in the carrying amount of goodwill (dollars in millions): Balance as of September 30, 2016 $ 2,467 Goodwill recorded in acquisition of Scottrade (see Note 2) 1,746 Balance as of September 30, 2017 4,213 Purchase accounting adjustments (1) 14 Balance as of September 30, 2018 $ 4,227 (1) The purchasing accounting adjustments are primarily attributable to post-closing adjustments related to the Bank Merger Consideration, property acquired and liabilities assumed in the acquisition of Scottrade. The purchase price allocation was finalized during September 2018, one-year from the anniversary of the Acquisition. Differences between purchase accounting estimates and actual results that arose prior to September 18, 2018 resulted in adjustments to the purchase price allocation. Any such adjustments arising on or after September 18, 2018 will be recorded in earnings. Acquired intangible assets consist of the following (dollars in millions): September 30, 2018 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Client relationships $ 2,183 $ (1,003 ) $ 1,180 $ 2,183 $ (877 ) $ 1,306 Technology and content 108 (108 ) — 108 (100 ) 8 Trade names 10 (7 ) 3 10 — 10 Trademark license 146 — 146 146 — 146 $ 2,447 $ (1,118 ) $ 1,329 $ 2,447 $ (977 ) $ 1,470 Amortization expense on acquired intangible assets was $141 million , $79 million and $86 million for fiscal years 2018 , 2017 and 2016 , respectively. Estimated future amortization expense for acquired finite-lived intangible assets outstanding as of September 30, 2018 is as follows (dollars in millions): Fiscal Year Estimated Amortization Expense 2019 $ 124 2020 116 2021 106 2022 105 2023 75 Thereafter (to 2035) 657 Total $ 1,183

Exit Liabilities

Exit Liabilities	12 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Exit Liabilities	Exit Liabilities As of September 18, 2017, the date of Acquisition, the Company began to incur costs in connection with actions taken to attain synergies from combining the operations of the Company and Scottrade. These costs, collectively referred to as "acquisition-related exit costs," include severance and other costs associated with consolidating facilities and administrative functions. As of September 30, 2018, substantially all of the acquisition-related exit costs associated with the Acquisition have been incurred. The following table summarizes activity in the Company's exit liabilities for the fiscal years ended September 30, 2018 and 2017, which are included in accounts payable and other liabilities on the Consolidated Balance Sheets (dollars in millions): Severance Pay and Other Employment Benefits Contract Termination and Other Costs Total Balance, September 30, 2016 $ 4 $ — $ 4 Exit liabilities assumed in business acquisition 100 — 100 Costs incurred and charged to expense 43 (1) 1 (2) 44 Costs paid or otherwise settled (9 ) (1 ) (10 ) Balance, September 30, 2017 138 — 138 Exit liabilities assumed - post closing adjustments — 9 9 Costs incurred and charged to expense 235 (1) 213 (2) 448 Costs paid or otherwise settled (352 ) (174 ) (526 ) Balance, September 30, 2018 $ 21 $ 48 $ 69 (1) Costs incurred for severance pay and other employment benefits are included in employee compensation and benefits on the Consolidated Statements of Income. (2) Costs incurred for contract termination and other costs are primarily included in other operating expense and professional services on the Consolidated Statements of Income. There were no material exit costs incurred which were not associated with the Scottrade acquisition during fiscal years 2018, 2017 and 2016. The following table summarizes the cumulative amount of acquisition related exit costs incurred by the Company related to the Scottrade acquisition as of September 30, 2018 (dollars in millions): Severance Pay and Other Employment Benefits Contract Termination and Other Costs Total Exit liabilities assumed in business acquisition $ 100 $ 9 $ 109 Employee compensation and benefits 267 — 267 Clearing and execution costs — 1 1 Communications — 1 1 Occupancy and equipment costs — 7 7 Professional services — 30 30 Other operating expense — 173 173 Other non-operating expense — 2 2 Total $ 367 $ 223 $ 590

Long-term Debt and Other Borrow

Long-term Debt and Other Borrowings	12 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Long-term Debt and Other Borrowings	Long-term Debt and Other Borrowings Long-term debt and other borrowings consist of the following (dollars in millions): September 30, 2018 Face Value Unamortized Discounts and Debt Issuance Costs Fair Value Adjustment (1) Net Carrying Value Other borrowings: Securities sold under agreements to repurchase $ 96 $ — $ — $ 96 Long-term debt: Senior Notes: 5.600% Notes due 2019 500 (1 ) 2 501 2.950% Notes due 2022 750 (4 ) (27 ) 719 3.625% Notes due 2025 500 (3 ) (17 ) 480 3.300% Notes due 2027 800 (9 ) (52 ) 739 Subtotal - Long-term debt 2,550 (17 ) (94 ) 2,439 Total long-term debt and other borrowings $ 2,646 $ (17 ) $ (94 ) $ 2,535 September 30, 2017 Face Value Unamortized Discounts and Debt Issuance Costs Fair Value Adjustment (1) Net Carrying Value Other borrowings: Securities sold under agreements to repurchase $ 97 $ — $ — $ 97 Long-term debt: Senior Notes: 5.600% Notes due 2019 500 (1 ) 15 514 2.950% Notes due 2022 750 (5 ) — 745 3.625% Notes due 2025 500 (3 ) 11 508 3.300% Notes due 2027 800 (9 ) (3 ) 788 Subtotal - Long-term debt 2,550 (18 ) 23 2,555 Total long-term debt and other borrowings $ 2,647 $ (18 ) $ 23 $ 2,652 (1) Fair value adjustments relate to changes in the fair value of the debt while in a fair value hedging relationship. See " Fair Value Hedging " below. Fiscal year maturities on long-term debt outstanding at September 30, 2018 are as follows (dollars in millions): 2019 $ — 2020 500 2021 — 2022 750 2023 — Thereafter 1,300 Total $ 2,550 Senior Notes — As of September 30, 2018 and 2017 , the Company had $2.55 billion aggregate principal amount of unsecured, fixed-rate Senior Notes due during calendar years 2019, 2022, 2025 and 2027 (together, the "Senior Notes"). The Company's Senior Notes were each sold through a public offering and pay interest semi-annually in arrears. Key information about the Senior Notes outstanding as of September 30, 2018 is summarized in the following table (dollars in millions): Description Date Issued Maturity Date Aggregate Principal Interest Rate 2019 Notes November 25, 2009 December 1, 2019 $500 5.600% 2022 Notes March 4, 2015 April 1, 2022 $750 2.950% 2025 Notes October 17, 2014 April 1, 2025 $500 3.625% 2027 Notes April 27, 2017 April 1, 2027 $800 3.300% The Company used the proceeds from the issuance of the 2027 Notes during fiscal year 2017 to finance a portion of the cash consideration paid by the Company in its acquisition of Scottrade. The 2022 Notes, 2025 Notes and 2027 Notes are not required to be guaranteed by any of the Company's subsidiaries. Prior to April 21, 2017, the 2019 Notes were required to be jointly, severally, fully and unconditionally guaranteed by each of the Company's current and future subsidiaries that was or became a borrower or a guarantor under the TD Ameritrade Holding Corporation Credit Agreement described below. As of April 21, 2017 , the obligations under the TD Ameritrade Holding Corporation Credit Agreement are no longer guaranteed by any subsidiary of the Parent; therefore the guarantee of the 2019 Notes was released. The Company may redeem the 2019 Notes, in whole at any time or in part from time to time, at a redemption price equal to the greater of (a) 100% of the principal amount of the notes being redeemed, and (b) the sum of the present values of the remaining scheduled payments of principal and interest on the notes being redeemed, discounted to the date of redemption on a semi-annual basis at the comparable U.S. Treasury rate, plus 35 basis points, plus accrued and unpaid interest to the date of redemption. The Company may redeem the 2022 Notes, 2025 Notes and 2027 Notes, in whole or in part, at any time prior to February 1, 2022 , January 1, 2025 and January 1, 2027 , respectively, at a redemption price equal to the greater of (a) 100% of the principal amount of the notes being redeemed, and (b) the sum of the present values of the remaining scheduled payments of principal and interest on the notes being redeemed, discounted to the date of redemption on a semi-annual basis at the comparable U.S. Treasury rate, plus 15 basis points in the case of the 2022 Notes, 25 basis points in the case of the 2025 Notes and 20 basis points in the case of the 2027 Notes, plus, in each case, accrued and unpaid interest to the date of redemption. The Company may redeem the 2022 Notes, 2025 Notes and 2027 Notes, in whole or in part, at any time on or after February 1, 2022 , January 1, 2025 and January 1, 2027 , respectively, at a redemption price equal to 100% of the principal amount of the notes being redeemed, plus, in each case, accrued and unpaid interest to the date of redemption. On October 30, 2018, the Company sold, through a public offering, an additional $1.0 billion aggregate principal amount of unsecured senior notes, consisting of both variable and fixed-rate notes. Key information regarding the recent debt issuance is summarized in the following table (dollars in millions): Description Date Issued Maturity Date Aggregate Principal Interest Rate 2021 Notes October 30, 2018 November 1, 2021 $600 Variable 2024 Notes October 30, 2018 April 1, 2024 $400 3.75% For additional details regarding the October 30, 2018 debt issuance, see Note 24, Subsequent Event. Lines of Credit — TD Ameritrade Clearing, Inc. ("TDAC"), a clearing broker-dealer subsidiary of the Company, utilizes secured uncommitted lines of credit for short-term liquidity. Under the secured uncommitted lines, TDAC borrows on a demand basis from two unaffiliated banks and pledges client margin securities as collateral. Advances under the secured uncommitted lines are dependent on having acceptable collateral as determined by each secured uncommitted credit agreement. At September 30, 2018, the terms of the secured uncommitted credit agreements do not specify borrowing limits. The availability of TDAC's secured uncommitted lines is subject to approval by the individual banks each time an advance is requested and may be denied. There were no borrowings outstanding under the secured uncommitted lines of credit as of September 30, 2018 . Securities Sold Under Agreements to Repurchase (repurchase agreements) — Under repurchase agreements, the Company receives cash from the counterparty and provides U.S. government debt securities as collateral. The Company's repurchase agreements generally mature between 30 and 90 days following the transaction date and are accounted for as secured borrowings. The remaining contractual maturity of the repurchase agreements with outstanding balances as of September 30, 2018 and 2017 was less than 30 days and 90 days, respectively. The weighted average interest rate on the balances outstanding as of September 30, 2018 and 2017 was 2.35% and 1.25% , respectively. See "General Contingencies" in Note 15 for a discussion of the potential risks associated with repurchase agreements and how the Company mitigates those risks. Fair Value Hedging — The Company is exposed to changes in the fair value of its fixed-rate Senior Notes resulting from interest rate fluctuations. To hedge this exposure, the Company has entered into fixed-for-variable interest rate swaps on each of the Senior Notes. Each fixed-for-variable interest rate swap has a notional amount and a maturity date matching the aggregate principal amount and maturity date, respectively, for each of the respective Senior Notes. The interest rate swaps effectively change the fixed-rate interest on the Senior Notes to variable-rate interest. Under the terms of the interest rate swap agreements, the Company receives semi-annual fixed-rate interest payments based on the same rates applicable to the Senior Notes, and makes quarterly variable-rate interest payments based on three-month LIBOR plus (a) 2.3745% for the swap on the 2019 Notes, (b) 0.9486% for the swap on the 2022 Notes, (c) 1.1022% for the swap on the 2025 Notes and (d) 1.0340% for the swap on the 2027 Notes. As of September 30, 2018 , the weighted average interest rate on the aggregate principal balance of the Senior Notes was 3.62% . The interest rate swaps are accounted for as fair value hedges and qualify for the shortcut method of accounting. Changes in the payment of interest resulting from the interest rate swaps are recorded in interest on borrowings on the Consolidated Statements of Income. Changes in fair value of the interest rate swaps are completely offset by changes in fair value of the related notes, resulting in no effect on net income. The following table summarizes gains and losses resulting from changes in the fair value of interest rate swaps designated as fair value hedges and the hedged fixed-rate debt for the fiscal years indicated (dollars in millions): 2018 2017 2016 Gain (loss) on fair value of interest rate swaps $ (117 ) $ (56 ) $ 16 Gain (loss) on fair value of hedged fixed-rate debt 117 56 (16 ) Net gain (loss) recorded in interest on borrowings $ — $ — $ — Cash Flow Hedging – On January 17, 2014 , the Company entered into forward-starting interest rate swap contracts with an aggregate notional amount of $500 million , to hedge against changes in the benchmark interest rate component of future interest payments resulting from an anticipated debt refinancing. The Company designated the contracts as a cash flow hedge of the future interest payments. Under cash flow hedge accounting, until settlement the swap contracts are carried at fair value and, to the extent they are an effective hedge, any unrealized gains or losses are recorded in other comprehensive income (loss). Any ineffective portion of the unrealized gains or losses is immediately recorded into earnings. Upon settlement, any realized gain or loss that has been recorded in other comprehensive income (loss) is amortized into earnings over the term of the newly-issued fixed-rate debt. On October 17, 2014, the Company sold $500 million of 2025 Notes as described under "Senior Notes" above, and paid approximately $45 million to settle the forward-starting interest rate swap contracts. As of September 30, 2018 , the Company expects to amortize $4.4 million of pre-tax losses, that were reported in accumulated other comprehensive loss, into interest on borrowings on the Consolidated Statements of Income within the next 12 months. Balance Sheet Impact of Hedging Instruments — The following table summarizes the classification and the fair value of outstanding derivatives designated as hedging instruments on the Consolidated Balance Sheets (dollars in millions): September 30, 2018 2017 Pay-variable interest rate swaps designated as fair value hedges: Other assets $ 2 $ 26 Accounts payable and other liabilities $ (96 ) $ (3 ) The interest rate swaps are subject to counterparty credit risk. Credit risk is managed by limiting activity to approved counterparties that meet a minimum credit rating threshold, by entering into credit support agreements, or by utilizing approved central clearing counterparties registered with the CFTC. The interest rate swaps require daily collateral coverage, in the form of cash or U.S. Treasury securities, for the aggregate fair value of the interest rate swaps (including accrued interest). As of September 30, 2018 and 2017 , the pay-variable interest rate swap counterparties had pledged $10 million and $40 million of collateral, respectively, to the Company in the form of cash. A liability for collateral pledged to the Company in the form of cash is recorded in accounts payable and other liabilities on the Consolidated Balance Sheets. As of September 30, 2018 and 2017 , the Company had pledged $82 million and $1 million of collateral, respectively, to the pay-variable interest rate swap counterparties in the form of cash. An asset for collateral pledged to the swap counterparties in the form of cash is recorded in other receivables on the Consolidated Balance Sheets. TD Ameritrade Holding Corporation Senior Revolving Credit Facilities — On April 21, 2017 , the Parent entered into a credit agreement consisting of a senior unsecured committed revolving credit facility in the aggregate principal amount of $300 million (the "Parent Revolving Facility"), replacing the Parent's prior $300 million unsecured revolving credit facility. The maturity date of the Parent Revolving Facility is April 21, 2022 . The obligations under the Parent Revolving Facility are not guaranteed by any subsidiary of Parent. TD Ameritrade Online Holdings Corp. ("TDAOH"), a wholly-owned subsidiary of the Company, guaranteed the Parent's obligations under the Parent's prior revolving credit facility and its 2019 Notes. Upon termination of the Parent's prior revolving credit facility on April 21, 2017 , TDAOH's guarantee of the 2019 Notes was also terminated. The applicable interest rate under the Parent Revolving Facility is calculated as a per annum rate equal to, at the option of the Parent, (a) LIBOR plus an interest rate margin ("Parent Eurodollar loans") or (b) (i) the highest of (x) the prime rate, (y) the federal funds effective rate (or, if the federal funds effective rate is unavailable, the overnight bank funding rate) plus 0.50% or (z) the eurodollar rate assuming a one-month interest period plus 1.00% , plus (ii) an interest rate margin ("ABR loans"). The interest rate margin ranges from 0.875% to 1.50% for Parent Eurodollar loans and from 0% to 0.50% for ABR loans, determined by reference to the Company's public debt ratings. The Parent is obligated to pay a commitment fee ranging from 0.08% to 0.20% on any unused amount of the Parent Revolving Facility, determined by reference to the Company's public debt ratings. There were no borrowings outstanding under the Parent Revolving Facility as of September 30, 2018 and 2017 . As of September 30, 2018 , the interest rate margin would have been 1.125% for Parent Eurodollar loans and 0.125% for ABR loans, and the commitment fee was 0.125% , each determined by reference to the Company's public debt ratings. The Parent Revolving Facility contains negative covenants that limit or restrict, subject to certain exceptions, the incurrence of liens, indebtedness of subsidiaries, mergers, consolidations, transactions with affiliates, change in nature of business and the sale of all or substantially all of the assets of the Company. The Parent is also required to maintain compliance with a maximum consolidated leverage ratio covenant and a minimum consolidated interest coverage ratio covenant, and the Company's broker-dealer and FCM/FDM subsidiaries are required to maintain compliance with a minimum regulatory net capital covenant. The Company was in compliance with all covenants under the Parent Revolving Facility as of September 30, 2018 . In addition to the Parent Revolving Facility, the Parent entered into a credit agreement on February 16, 2018, consisting of a senior unsecured committed revolving credit facility in the aggregate principal amount of $500 million , with substantially the same terms as the Parent Revolving Facility. The February 16, 2018 revolving credit facility matured on May 17, 2018. TD Ameritrade Clearing, Inc. Senior Revolving Credit Facilities — TDAC has access to two senior unsecured committed revolving credit facilities with an aggregate principal amount of $1.45 billion , consisting of a $600 million (the " $600 Million Revolving Facility") and an $850 million (the " $850 Million Revolving Facility") senior revolving facility (together, the "TDAC Revolving Facilities") entered into on April 21, 2017 and May 17, 2018, respectively. The maturity dates of the $600 Million Revolving Facility and the $850 Million Revolving Facility are April 21, 2022 and May 16, 2019, respectively. The applicable interest rate under each of the TDAC Revolving Facilities is calculated as a per annum rate equal to, at the option of TDAC, (a) LIBOR plus an interest rate margin ("TDAC Eurodollar loans") or (b) the federal funds effective rate plus an interest rate margin ("Federal Funds Rate loans"). The interest rate margin ranges from 0.75% to 1.25% for both TDAC Eurodollar loans and Federal Funds Rate loans, determined by reference to the Company's public debt ratings. TDAC is obligated to pay commitment fees ranging from 0.07% to 0.175% and from 0.06% to 0.125% on any unused amounts of the $600 Million Revolving Facility and the $850 Million Revolving Facility, respectively, each determined by reference to the Company's public debt ratings. There were no borrowings outstanding under the TDAC Revolving Facilities as of September 30, 2018 and 2017 . As of September 30, 2018 , the interest rate margin under the TDAC Revolving Facilities would have been 1.00% for both TDAC Eurodollar loans and Federal Funds Rate loans, determined by reference to the Company's public debt ratings. As of September 30, 2018 , the commitment fees under the $600 Million Revolving Facility and the $850 Million Revolving Facility were 0.10% and 0.08% , respectively, each determined by reference to the Company's public debt ratings. The TDAC Revolving Facilities contain negative covenants that limit or restrict, subject to certain exceptions, the incurrence of liens, indebtedness of TDAC, mergers, consolidations, change in nature of business and the sale of all or substantially all of the assets of TDAC. TDAC is also required to maintain minimum tangible net worth and is required to maintain compliance with minimum regulatory net capital requirements, which may change from time to time. TDAC was in compliance with all covenants under the TDAC Revolving Facilities as of September 30, 2018 . TD, along with other financial institutions, is participating as a lender under the Parent Revolving Facility and the TDAC Revolving Facilities. As of September 30, 2018 and 2017 , the total lending commitment received from TD under these credit facilities was $257 million and $115 million , respectively. For additional information regarding the Company's transactions with TD, see Note 21, Related Party Transactions. Intercompany Credit Agreements — The Parent has entered into credit agreements with each of its primary broker-dealer and FCM/FDM subsidiaries, under which the Parent may make loans of cash or securities under committed and/or uncommitted lines of credit. Key information about the committed and/or uncommitted lines of credit is summarized in the following table (dollars in millions): Borrower Subsidiary Committed Facility Uncommitted Facility (1) Termination Date TD Ameritrade Clearing, Inc. $400 $300 March 1, 2022 TD Ameritrade, Inc. N/A $300 March 1, 2022 TD Ameritrade Futures & Forex LLC $45 N/A August 11, 2021 (1) The Parent is permitted, but under no obligation, to make loans under uncommitted facilities. Loans under both the committed and uncommitted facilities bear interest at the same rate as borrowings under the TDAC Revolving Facilities and must be repaid with interest on or before the termination date. There were no borrowings outstanding under any of the intercompany credit agreements as of September 30, 2018 and 2017 .

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Tax Cuts and Jobs Act was enacted on December 22, 2017. The Act reduces the U.S. federal corporate income tax rate from 35% to 21%, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. As of September 30, 2018, the Company has completed its accounting for the tax effects of the Act. The U.S. federal statutory income tax rate, for companies with a fiscal year end of September 30, 2018, was a blended rate of 24.5% . However, as the Company is on a calendar year for tax reporting purposes, the actual computed blended U.S. federal statutory income tax rate was somewhat lower due to the Company's income being earned unevenly during the fiscal year. Provision for income taxes is comprised of the following for the fiscal years indicated (dollars in millions): 2018 2017 2016 Current expense (benefit): Federal $ 380 $ 484 $ 435 State 58 49 (4 ) 438 533 431 Deferred expense (benefit): Federal (32 ) (11 ) (5 ) State 8 — (3 ) (24 ) (11 ) (8 ) Provision for income taxes $ 414 $ 522 $ 423 A reconciliation of the U.S. federal statutory income tax rate to the effective tax rate applicable to pre-tax income follows for the fiscal years indicated: 2018 2017 2016 Federal statutory income tax rate 24.5 % 35.0 % 35.0 % Statutory versus actual blended federal income tax rate (1.3 ) — — State taxes, net of federal tax effect 2.6 2.8 2.8 Adjustments to estimated state income taxes — — (0.2 ) Federal incentives 0.4 (0.3 ) (1.4 ) Interest recorded (reversed) on unrecognized tax benefits, net 0.2 0.2 (1.1 ) Remeasurement of U.S. deferred income taxes (3.8 ) — — Reversal of accruals for unrecognized tax benefits (0.4 ) (0.4 ) (1.8 ) Share-based payment compensation (0.3 ) — — Other — 0.1 0.1 21.9 % 37.4 % 33.4 % The Company's effective income tax rate for fiscal year 2018 was 21.9% , compared to 37.4% and 33.4% for fiscal years 2017 and 2016 , respectively. The provision for income taxes for fiscal year 2018 included a net favorable adjustment of $71 million related to the remeasurement of the Company's deferred income tax balances as it pertains to the Act, a $5 million income tax benefit resulting from the change in accounting for income taxes related to equity-based compensation under ASU 2016-09, $12 million of favorable resolutions of state income tax matters and a $30 million favorable benefit resulting from accelerating certain deductions, including acquisition-related exit costs, to leverage higher 2017 pre-enactment tax rates. The effective income tax rate was also impacted by a $9 million unfavorable remeasurement of uncertain tax positions related to certain federal incentives. These items had a net favorable impact on the Company's earnings for fiscal year 2018 of approximately $0.19 per share. The provision for income taxes for fiscal year 2017 included $8 million of net favorable resolutions of state income tax matters and $4 million of favorable tax benefits for certain federal incentives. These items had a net favorable impact on the Company's earnings for fiscal year 2017 of approximately two cents per share. The provision for income taxes for fiscal year 2016 was impacted by $39 million of net favorable adjustments to uncertain tax positions and related deferred income tax assets, which included a favorable $33 million tax liability remeasurement related to a state court decision. The provision was also impacted by an $18 million favorable tax benefit claimed during fiscal year 2016 for federal deductions and tax credits related to calendar tax year 2012 through September 30, 2016 and $5 million of net favorable deferred income tax adjustments due to the remeasurement of deferred tax assets and liabilities and the cumulative impact of the decline in the state tax rate. These items had a net favorable impact on the Company's earnings for fiscal year 2016 of approximately $0.12 per share. Deferred tax assets (liabilities) are comprised of the following (dollars in millions): September 30, 2018 2017 Deferred tax assets: Accrued and other liabilities $ 78 $ 131 Stock-based compensation 19 28 Allowance for doubtful accounts 14 6 Unrecognized loss on cash flow hedging instruments 9 15 Intangible assets, state tax benefit 3 5 Operating loss carryforwards 2 1 Gross deferred tax assets 125 186 Less: Valuation allowance (2 ) (1 ) Net deferred tax assets 123 185 Deferred tax liabilities: Acquired intangible assets (236 ) (331 ) Property and equipment (46 ) (35 ) Prepaid expenses (13 ) (11 ) Unrealized gain on investments (2 ) — Other deferred tax liabilities (3 ) (1 ) Total deferred tax liabilities (300 ) (378 ) Net deferred tax liabilities $ (177 ) $ (193 ) At September 30, 2018 , subsidiaries of the Company have approximately $35 million of separate state operating loss carryforwards. These carryforwards expire between fiscal years 2021 and 2037 . Because the realization of the tax benefit from state loss carryforwards is dependent on certain subsidiaries generating sufficient state taxable income in future periods, as well as annual limitations on future utilization, the Company has provided a valuation allowance against the computed benefit in order to reflect the tax benefit expected to be realized. A reconciliation of the activity related to unrecognized tax benefits follows for the fiscal years indicated (dollars in millions): 2018 2017 2016 Beginning balance $ 152 $ 142 $ 154 Additions based on tax positions related to the current year 35 28 30 Additions for tax positions of prior years 8 — 20 Reductions due to lapsed statute of limitations (9 ) (7 ) (8 ) Reductions due to settlements with taxing authorities (3 ) (1 ) (21 ) Reductions for tax positions of prior years (2 ) (10 ) (33 ) Ending balance $ 181 $ 152 $ 142 The balance of unrecognized tax benefits as of September 30, 2018 was $181 million ( $151 million net of the federal benefit on state matters), all of which, if recognized, would favorably affect the effective income tax rate in any future periods. The balance of unrecognized tax benefits as of September 30, 2017 was $152 million ( $108 million net of the federal benefit on state matters), all of which, if recognized, would favorably affect the effective income tax rate in any future periods. The Company's income tax returns are subject to review and examination by federal, state and local taxing authorities. The Company's federal claims for refund for tax years 2012 through 2014 are being examined by the Internal Revenue Service. The federal returns for 2015 through 2017 remain open under the statute of limitations. The years open to examination by state and local government authorities vary by jurisdiction, but the statute of limitations is generally three to four years from the date the tax return is filed. It is reasonably possible that the gross unrecognized tax benefits as of September 30, 2018 could decrease by up to $77 million ( $67 million net of the federal benefit on state matters) within the next 12 months as a result of settlements of certain examinations or expiration of the statute of limitations with respect to other tax filings. The Company recognized $4 million and $2 million of interest and penalties expense (net of the federal benefit) on the Consolidated Statements of Income for fiscal years 2018 and 2017, respectively, primarily due to accruals for unrecognized tax benefits. The Company recognized $17 million of net benefits for interest and penalties (net of the federal income tax effect) for fiscal year 2016, primarily due to favorable resolutions and remeasurement of uncertain tax positions. As of September 30, 2018 and 2017 , accrued interest and penalties related to unrecognized tax benefits was $30 million and $26 million , respectively.

Capital Requirements

Capital Requirements	12 Months Ended
	Sep. 30, 2018
Regulatory Capital Requirements [Abstract]
Capital Requirements	Capital Requirements The Company's broker-dealer subsidiaries are subject to the SEC Uniform Net Capital Rule (Rule 15c3-1 under the Exchange Act), administered by the SEC and FINRA, which requires the maintenance of minimum net capital, as defined. Net capital and the related net capital requirement may fluctuate on a daily basis. TDAC, the Company's clearing broker-dealer subsidiary, and TD Ameritrade, Inc., an introducing broker-dealer subsidiary of the Company, compute net capital under the alternative method as permitted by Rule 15c3-1. TDAC is required to maintain minimum net capital of the greater of $1.5 million , which is based on the type of business conducted by the broker-dealer, or 2% of aggregate debit balances arising from client transactions. TD Ameritrade, Inc.is required to maintain minimum net capital of the greater of $250,000 or 2% of aggregate debit balances. In addition, under the alternative method, a broker-dealer may not repay any subordinated borrowings, pay cash dividends or make any unsecured advances or loans to its parent company or employees if such payment would result in net capital of less than (a) 5% of aggregate debit balances or (b) 120% of its minimum dollar requirement. TDAFF, the Company's FCM and FDM subsidiary registered with the CFTC, is subject to CFTC Regulations 1.17 and 5.7 under the Commodity Exchange Act, administered by the CFTC and the NFA. As an FCM, TDAFF is required to maintain minimum adjusted net capital under CFTC Regulation 1.17 of the greater of (a) $1.0 million or (b) its futures risk-based capital requirement, equal to 8% of the total risk margin requirement for all futures positions carried by the FCM in client and nonclient accounts. As an FDM, TDAFF is also subject to the net capital requirements under CFTC Regulation 5.7, which requires TDAFF to maintain minimum adjusted net capital of the greater of (a) any amount required under CFTC Regulation 1.17 as described above or (b) $20.0 million plus 5% of all foreign exchange liabilities owed to forex clients in excess of $10.0 million . In addition, an FCM and FDM must provide notice to the CFTC if its adjusted net capital amounts to less than (a) 110% of its risk-based capital requirement under CFTC Regulation 1.17, (b) 150% of its $1.0 million minimum dollar requirement, or (c) 110% of $20.0 million plus 5% of all foreign exchange liabilities owed to forex clients in excess of $10.0 million . Net capital and net capital requirements for the Company's broker-dealer subsidiaries are summarized in the following tables (dollars in millions): TD Ameritrade Clearing, Inc. Date Net Capital Required Net Capital (2% of Aggregate Debit Balances) Net Capital in Excess of Required Net Capital Ratio of Net Capital to Aggregate Debit Balances September 30, 2018 $ 2,831 $ 525 $ 2,306 10.79 % September 30, 2017 $ 1,595 $ 340 $ 1,255 9.39 % TD Ameritrade, Inc. Date Net Capital Required Net Capital (Minimum Dollar Requirement) Net Capital in Excess of Required Net Capital September 30, 2018 $ 181 $ 0.25 $ 181 September 30, 2017 $ 155 $ 0.25 $ 155 Scottrade, Inc. Date Net Capital Required Net Capital (2% of Aggregate Debit Balances) Net Capital in Excess of Required Net Capital Ratio of Net Capital to Aggregate Debit Balances September 30, 2018 (1) N/A N/A N/A N/A September 30, 2017 $ 348 $ 70 $ 278 9.99 % (1) On February 26, 2018, Scottrade, Inc. transferred substantially all of its broker-dealer business net assets, including its clearing operations, to other subsidiaries of the Company. The Company's request to withdraw Scottrade, Inc.'s registration as a broker-dealer was granted and the withdrawal became effective on September 7, 2018. Adjusted net capital and adjusted net capital requirements for the Company's FCM and FDM subsidiary are summarized in the following table (dollars in millions): TD Ameritrade Futures & Forex LLC Date Adjusted Net Capital Required Adjusted Net Capital ($20 Million Plus 5% of All Foreign Exchange Liabilities Owed to Forex Clients in Excess of $10 Million) Adjusted Net Capital in Excess of Required Adjusted Net Capital September 30, 2018 $ 129 $ 23 $ 106 September 30, 2017 $ 77 $ 22 $ 55 The Company's non-depository trust company subsidiary, TD Ameritrade Trust Company ("TDATC"), is subject to capital requirements established by the State of Maine, which require TDATC to maintain minimum Tier 1 capital, as defined. TDATC's Tier 1 capital was $39 million and $32 million as of September 30, 2018 and 2017 , respectively, which exceeded the required Tier 1 capital by $18 million and $13 million , respectively.

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based Compensation	Stock-based Compensation The Company has two stock incentive plans under which Company stock-based awards may be granted: the TD Ameritrade Holding Corporation Long-Term Incentive Plan (the "LTIP") and the 2006 Directors Incentive Plan (the "Directors Plan"). The LTIP authorizes the award of options to purchase common stock, common stock appreciation rights, restricted stock, restricted stock units, performance shares and performance units. Under the LTIP, 42,104,174 shares of the Company's common stock are reserved for issuance to eligible employees, consultants and non-employee directors. The Directors Plan authorizes the award of options to purchase common stock, common stock appreciation rights, restricted stock units and restricted stock. Under the Directors Plan, 1,830,793 shares of the Company's common stock are reserved for issuance to non-employee directors. Stock options, except for replacement options granted in connection with business combinations, are granted by the Company with an exercise price not less than the fair market value of the Company's common stock on the grant date. Stock options generally vest over a one - to four -year period and expire 10 years after the grant date. Restricted stock units ("RSUs") are awards that entitle the holder to receive shares of Company common stock following a vesting period. RSUs granted to employees generally vest after the completion of a three -year period or ratably over a three -year period. RSUs granted to non-employee directors generally vest over a one -year period. Performance-based restricted stock units ("PRSUs") are a form of RSUs in which the number of shares ultimately received depends on how the Company's total shareholder return compares to the total shareholder returns of companies in a selected performance peer group. PRSUs are subject to a three -year cliff vesting period. At the end of the performance period, the number of shares of common stock issued can range from 80% to 120% of target, depending on the Company's ranking in the performance peer group. Shares of common stock are issued following the end of the performance period. Stock-based compensation expense was $60 million , $36 million and $34 million for fiscal years 2018, 2017 and 2016, respectively. The related income tax benefits were $17 million , $14 million and $13 million for fiscal years 2018, 2017 and 2016, respectively. The following is a summary of option activity in the Company's stock incentive plans for the fiscal year ended September 30, 2018 : Number of Options (in thousands) Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in millions) Outstanding at beginning and end of year 503 $ 27.97 7.3 $ 13 Exercisable at end of year 252 $ 27.97 7.3 $ 6 The weighted-average grant-date fair value of options granted during fiscal year 2016 was $6.16 . No options were granted during fiscal years 2018 and 2017 . The total intrinsic value of options exercised during fiscal years 2017 and 2016 was $26 million and $0.1 million , respectively. No options were exercised during fiscal year 2018. As of September 30, 2018 , the total unrecognized compensation cost related to nonvested stock options awards was $1 million and was expected to be recognized over a weighted-average period of 1.3 years. The fair value of stock options granted during fiscal year 2016 was estimated using a Black-Scholes-Merton valuation model with the following inputs: Risk-free interest rate 1.73 % Expected dividend yield 2.4 % Expected volatility 27 % Expected option life (years) 6.5 The risk-free interest rate input was based on U.S. Treasury note yields with remaining terms comparable to the expected option life input used in the valuation model. The expected dividend yield was based on the annual dividend yield at the time of grant. The expected volatility was based on historical daily price changes of the Company's stock since July 2009. The expected option life was the average number of years that the Company estimated the options will be outstanding, based primarily on historical employee option exercise behavior. The Company measures the fair value of RSUs based upon the volume-weighted average market price of the underlying common stock as of the date of grant. The grant date fair value of PRSUs was determined based upon a Monte Carlo simulation model whereby the stock prices of the Company and the selected peer group companies were simulated using correlated Geometric Brownian motion paths in order to estimate the Company's total expected shareholder return rank within the peer group index and the corresponding percent of PRSUs that are estimated to be earned per the PRSU award agreement. RSUs and PRSUs are amortized over their applicable vesting period using the straight-line method, reduced by expected forfeitures. The following is a summary of RSU activity in the Company's stock incentive plans for the fiscal year ended September 30, 2018 : Number of Units (in thousands) Weighted Average Grant Date Fair Value Nonvested at beginning of year 2,394 $ 34.83 Granted 671 $ 50.61 Vested (807 ) $ 33.24 Forfeited (129 ) $ 41.72 Nonvested at end of year 2,129 $ 39.99 The weighted-average grant-date fair value of RSUs granted during fiscal years 2018, 2017 and 2016 was $50.61 , $40.66 and $27.97 , respectively. As of September 30, 2018 , there was $31 million of estimated unrecognized compensation cost related to nonvested RSUs, which was expected to be recognized over a weighted average period of 1.9 years. The total fair value of RSUs that vested during fiscal years 2018 , 2017 and 2016 was $42 million , $70 million and $71 million , respectively. The following is a summary of PRSU activity in the Company's stock incentive plans for the fiscal year ended September 30, 2018 : Number of Units (in thousands) Weighted Average Grant Date Fair Value Nonvested at beginning of year 265 $ 39.48 Granted 235 $ 49.50 Nonvested at end of year 500 $ 44.19 The weighted-average grant-date fair value of the PRSUs granted during the fiscal years 2018 and 2017 was $49.50 and $39.48 , respectively. As of September 30, 2018 , there was $9 million of estimated unrecognized compensation cost related to nonvested PRSUs, which was expected to be recognized over a weighted average period of 1.9 years. No PRSUs were granted during fiscal year 2016. The fair value of PRSUs granted was estimated using a Monte Carlo simulation model with the following inputs for the fiscal years indicated: 2018 2017 Risk-free interest rate 1.84 % 1.34 % Expected dividend yield 0 % 0 % Expected volatility 28 % 27 % Expected term (years) 2.8 2.9 The risk-free interest rate input was based on U.S. Treasury note yields with remaining terms comparable to the expected term input used in the valuation model. The expected dividend yield was selected to be zero as the vesting condition is based on total shareholder return, which includes changes in price, plus reinvestment of dividends paid. The expected volatility was based on historical daily price changes for a period of time that corresponds with the expected term input used in the valuation model. The expected term input was based on the contractual remaining period of time until the award vests in accordance with the PRSU award agreement. Although the Company does not have a formal policy regarding issuance of shares for stock-based compensation, such shares are generally issued from treasury stock. The stockholders agreement entered into in connection with the acquisition of TD Waterhouse Group, Inc. requires the Company to repurchase its common stock from time to time to offset dilution resulting from stock option exercises and other stock awards subsequent to the acquisition. As of September 30, 2018 , the Company was not obligated to repurchase additional shares pursuant to the stockholders agreement. The Company cannot estimate the amount and timing of repurchases that may be required as a result of future stock issuances.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Sep. 30, 2018
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans The Company has a 401(k) and profit-sharing plan under which annual profit-sharing contributions are determined at the discretion of the board of directors. The Company also makes matching contributions pursuant to the plan document. Profit-sharing and matching contributions expense was $53 million , $38 million and $35 million for fiscal years 2018 , 2017 and 2016 , respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Lease Commitments — The Company has various non-cancelable operating leases on facilities requiring annual payments as follows (dollars in millions): Fiscal Year Minimum Lease Payments Sublease Income Net Lease Commitments 2019 $ 75 $ (1 ) $ 74 2020 64 (1 ) 63 2021 45 — 45 2022 34 — 34 2023 28 — 28 Thereafter (to 2033) 99 — 99 Total $ 345 $ (2 ) $ 343 A majority of the leases for the Company's branch offices contain provisions for renewal at the Company's option. Rental expense, net of sublease income, was approximately $83 million , $54 million and $51 million for fiscal years 2018 , 2017 and 2016 , respectively. Legal and Regulatory Matters Order Routing Matters — In 2014, five putative class action complaints were filed regarding TD Ameritrade, Inc.'s routing of client orders and one putative class action was filed regarding Scottrade, Inc.'s routing of client orders. Five of the six cases were dismissed and the United States Court of Appeals, 8 th Circuit, affirmed the dismissals in those cases that were appealed. The one remaining case is Roderick Ford (replacing Gerald Klein) v. TD Ameritrade Holding Corporation, et al. , Case No. 8:14CV396 (U.S. District Court, District of Nebraska). Plaintiff alleges that, when routing client orders to various market centers, defendants did not seek best execution, and instead routed clients' orders to market venues that pay TD Ameritrade, Inc. the most money for order flow. Plaintiff alleges that defendants made misrepresentations and omissions regarding the Company's order routing practices. The complaint asserts claims of violation s of Section 10(b) and 20 of the Exchange Act and SEC Rule 10b-5. The complaint seeks damages, injunctive relief, and other relief. Plaintiff filed a motion for class certification, which defendants opposed. On July 12, 2018, the Magistrate Judge issued findings and a recommendation that plaintiffs' motion for class certification be denied. Plaintiff filed objections to the Magistrate Judge's findings and recommendation, which defendants opposed. On September 14, 2018, the District Judge sustained plaintiff's objections, rejected the Magistrate Judge's recommendation and granted plaintiff's motion for class certification. On September 28, 2018, defendants filed a petition requesting that the U.S. Court of Appeals, 8th Circuit, grant an immediate appeal of the District Court's class certification decision. The Securities Industry and Financial Markets Association and the U.S. Chamber of Commerce filed amicus curiae briefs in support of the petition together with motions for permission to file the briefs. On October 9, 2018, plaintiff filed an opposition to the petition. The Company intends to vigorously defend against this lawsuit and is unable to predict the outcome or the timing of the ultimate resolution of the lawsuit, or the potential loss, if any, that may result. Certain regulatory authorities are conducting examinations and investigations regarding the routing of client orders. TD Ameritrade, Inc., TDAC and Scottrade, Inc. have received requests for documents and information from the regulatory authorities. TD Ameritrade, Inc., TDAC and Scottrade, Inc. are cooperating with the requests. Lawsuit regarding Scottrade Acquisition — On April 6, 2017, a stockholder of the Company filed a stockholder derivative complaint regarding the acquisition of Scottrade by the Company and the acquisition of Scottrade Bank by TD. The suit filed in the Delaware Chancery Court is captioned Vero Beach Police Officers' Retirement Fund, derivatively on behalf of nominal defendant TD Ameritrade Holding Corp. v. Larry Bettino et al ., C.A. No. 2017-0264-JRS. On December 18, 2017, the plaintiff filed an amended complaint. The suit names as defendants TD and the members of the Company's board of directors. It also names the Company as a nominal defendant. The complaint alleges that the Company's acquisition of Scottrade and TD's acquisition of Scottrade Bank were unfair from the perspective of the Company because TD Bank, N.A. acquired Scottrade Bank for an allegedly low price, which in turn caused the Company to pay an allegedly high price to acquire Scottrade. The complaint claims that the Company's directors and TD, as the Company's alleged controlling stockholder, breached their fiduciary duties to the Company and its stockholders, and that TD aided and abetted the Company directors' breach of fiduciary duty and was unjustly enriched. The complaint seeks a declaration that demand on the Company's board is excused as futile and seeks corporate governance reforms, damages, interest and fees. On August 9, 2018, the parties submitted to the court for its approval a stipulation of settlement of this action. Under the proposed settlement, TD and an insurer on behalf of the Company's directors will make a settlement payment of an immaterial amount; plaintiff may apply for an award of attorneys' fees and expenses in an amount not to exceed 20% of the settlement payment; the balance of the settlement payment will be paid to the Company; and the lawsuit will be dismissed and the claims will be released. A hearing on approval of the settlement and an award of attorneys' fees and expenses is scheduled for December 3, 2018. There can be no assurance that the proposed settlement will be finalized and approved by the court. If the proposed settlement is not finalized or approved by the court, the Company will be unable to predict the outcome or the timing of the ultimate resolution of this lawsuit, or the potential losses, if any, that may result. Aequitas Securities Litigation — An amended putative class action complaint was filed in the U.S. District Court for the District of Oregon in Lawrence Ciuffitelli et al. v. Deloitte & Touche LLP, EisnerAmper LLP, Sidley Austin LLP, Tonkon Torp LLP, TD Ameritrade, Inc., and Integrity Bank & Trust, Case No. 3:16CV580, on May 19, 2016. A second amended putative class action complaint was filed on September 8, 2017, in which Duff & Phelps was added as a defendant. The putative class includes all persons who purchased securities of Aequitas Commercial Finance, LLC and its affiliates on or after June 9, 2010. Other groups of plaintiffs have filed five non-class action lawsuits in Oregon Circuit Court, Multnomah County, against these and other defendants: Walter Wurster, et al. v. Deloitte & Touche et al. , Case No. 16CV25920 (filed Aug. 11, 2016), Kenneth Pommier, et al. v. Deloitte & Touche et al., Case No. 16CV36439 (filed Nov. 3, 2016), Charles Ramsdell, et al. v. Deloitte & Touche et al., Case No. 16CV40659 (filed Dec. 2, 2016), Charles Layton, et al. v. Deloitte & Touche et al., Case No. 17CV42915 (filed October 2, 2017) and John Cavanagh, et al. v. Deloitte & Touche et al., Case No. 18CV09052 (filed March 7, 2018). FINRA arbitrations have also been filed against TD Ameritrade, Inc. The claims in these actions include allegations that the sales of Aequitas securities were unlawful, the defendants participated and materially aided in such sales in violation of the Oregon securities laws, and material misstatements and omissions were made. While the factual allegations differ in various respects among the cases, plaintiffs' allegations include assertions that: TD Ameritrade customers purchased more than $140 million of Aequitas securities; TD Ameritrade served as custodian for Aequitas securities; recommended and referred investors to financial advisors as part of its advisor referral program for the purpose of purchasing Aequitas securities; participated in marketing the securities; recommended the securities; provided assurances to investors about the safety of the securities; and developed a market for the securities. In the Ciuffitelli putative class action, plaintiffs allege that more than 1,500 investors were owed more than $600 million on the Aequitas securities they purchased. On August 1, 2018, the Magistrate Judge in that case issued findings and a recommendation that defendants' motions to dismiss the pending complaint be denied with limited exceptions not applicable to the Company. TD Ameritrade and other defendants filed objections to the Magistrate Judge's findings and recommendation, which plaintiffs opposed. On September 24, 2018, the District Judge issued an opinion and order adopting the Magistrate Judge's findings and recommendation. Discovery has commenced. In the five non-class action lawsuits, approximately 200 named plaintiffs collectively allege a total of approximately $125 million in losses plus other damages. In the Wurster and Pommier cases, the Court, on TD Ameritrade's motion, dismissed the claims by those plaintiffs who were TD Ameritrade customers, in favor of arbitration. Discovery is ongoing. The Court in the Wurster and Pommier cases denied TD Ameritrade's motion to dismiss the claims by the plaintiffs who were not TD Ameritrade customers. Plaintiffs in the Ramsdell case have filed a second amended complaint in which TD Ameritrade is not named as a defendant. On September 24, 2018, plaintiffs in the Cavanagh case dismissed their claims against TD Ameritrade. On July 17, 2018, plaintiffs in the Ciuffitelli case filed a motion for preliminary approval of an $18.5 million settlement with the defendant Tonkon Torp law firm of the claims against it in all the pending cases. On September 24, 2018, defendants filed a response requesting the Court to defer considering the plaintiffs' motion or to deny it as presented. The Company intends to vigorously defend against this litigation. The Company is unable to predict the outcome or the timing of the ultimate resolution of this litigation, or the potential losses, if any, that may result. Other Legal and Regulatory Matters — The Company is subject to a number of other lawsuits, arbitrations, claims and other legal proceedings in connection with its business. Some of these legal actions include claims for substantial or unspecified compensatory and/or punitive damages. In addition, in the normal course of business, the Company discusses matters with its regulators raised during regulatory examinations or otherwise subject to their inquiry. These matters could result in censures, fines, penalties or other sanctions. ASC 450, Loss Contingencies , governs the recognition and disclosure of loss contingencies, including potential losses from legal and regulatory matters. ASC 450 categorizes loss contingencies using three terms based on the likelihood of occurrence of events that result in a loss: "probable" means that "the future event or events are likely to occur;" "remote" means that "the chance of the future event or events occurring is slight;" and "reasonably possible" means that "the chance of the future event or events occurring is more than remote but less than likely." Under ASC 450, the Company accrues for losses that are considered both probable and reasonably estimable. The Company may incur losses in addition to the amounts accrued where the losses are greater than estimated by management, or for matters for which an unfavorable outcome is considered reasonably possible, but not probable. The Company estimates that the aggregate range of reasonably possible losses in excess of amounts accrued is from $0 to $175 million as of September 30, 2018 . This estimated aggregate range of reasonably possible losses is based upon currently available information for those legal and regulatory matters in which the Company is involved, taking into account the Company's best estimate of reasonably possible losses for those matters as to which an estimate can be made. For certain matters, the Company does not believe an estimate can currently be made, as some matters are in preliminary stages and some matters have no specific amounts claimed. The Company's estimate involves significant judgment, given the varying stages of the proceedings and the inherent uncertainty of predicting outcomes. The estimated range will change from time to time as the underlying matters, stages of proceedings and available information change. Actual losses may vary significantly from the current estimated range. The Company believes, based on its current knowledge and after consultation with counsel, that the ultimate disposition of these legal and regulatory matters, individually or in the aggregate, is not likely to have a material adverse effect on the financial condition or cash flows of the Company. However, in light of the uncertainties involved in such matters, the Company is unable to predict the outcome or the timing of the ultimate resolution of these matters, or the potential losses, fines, penalties or equitable relief, if any, that may result, and it is possible that the ultimate resolution of one or more of these matters may be material to the Company's results of operations for a particular reporting period. Income Taxes The Company's federal and state income tax returns are subject to examination by taxing authorities. Because the application of tax laws and regulations to many types of transactions is subject to varying interpretations, amounts reported in the consolidated financial statements could be significantly changed at a later date upon final determinations by taxing authorities. General Contingencies In the ordinary course of business, there are various contingencies that are not reflected in the consolidated financial statements. These include the Company's broker-dealer and FCM/FDM subsidiaries' client activities involving the execution, settlement and financing of various client securities, options, futures and foreign exchange transactions. These activities may expose the Company to credit risk in the event the clients are unable to fulfill their contractual obligations. The Company extends margin credit and leverage to its clients. In margin transactions, the Company extends credit to the client, subject to various regulatory and internal margin requirements, collateralized by cash and securities in the client's account. In connection with these activities, the Company also routes client orders for execution and clears client transactions involving the sale of securities not yet purchased ("short sales"). Such margin-related transactions may expose the Company to credit risk in the event a client's assets are not sufficient to fully cover losses that the client may incur. Leverage involves securing a large potential future obligation with a lesser amount of collateral. The risks associated with margin credit and leverage increase during periods of rapid market movements, or in cases where leverage or collateral is concentrated and market movements occur. In the event the client fails to satisfy its obligations, the Company has the authority to liquidate certain positions in the client's account at prevailing market prices in order to fulfill the client's obligations. However, during periods of rapid market movements, clients who utilize margin credit or leverage and who have collateralized their obligations with securities may find that the securities have a rapidly depreciating value and may not be sufficient to cover their obligations in the event of liquidation. The Company seeks to mitigate the risks associated with its client margin and leverage activities by requiring clients to maintain margin collateral in compliance with various regulatory and internal guidelines. The Company monitors required margin levels throughout each trading day and, pursuant to such guidelines, requires clients to deposit additional collateral, or to reduce positions, when necessary. The Company contracts with unaffiliated FCM, FDM and broker-dealer entities to clear and execute futures and foreign exchange transactions for its clients. This can result in concentrations of credit risk with one or more of these counterparties. This risk is partially mitigated by the counterparties' obligation to comply with rules and regulations governing FCMs, FDMs and broker-dealers in the United States. These rules generally require maintenance of net capital and segregation of client funds and securities. In addition, the Company manages this risk by requiring credit approvals for counterparties and by utilizing account funding and sweep arrangement agreements that generally specify that all client cash in excess of futures funding requirements be transferred back to the clients' securities brokerage accounts at the Company on a daily basis. The Company loans securities temporarily to other broker-dealers in connection with its broker-dealer business. The Company receives cash as collateral for the securities loaned. Increases in securities prices may cause the market value of the securities loaned to exceed the amount of cash received as collateral. In the event the counterparty to these transactions does not return the loaned securities, the Company may be exposed to the risk of acquiring the securities at prevailing market prices in order to satisfy its client obligations. The Company mitigates this risk by requiring credit approvals for counterparties, by monitoring the market value of securities loaned on a daily basis and requiring additional cash as collateral when necessary, and by participating in a risk-sharing program offered through the Options Clearing Corporation ("OCC"). The Company borrows securities temporarily from other broker-dealers in connection with its broker-dealer business. The Company deposits cash as collateral for the securities borrowed. Decreases in securities prices may cause the market value of the securities borrowed to fall below the amount of cash deposited as collateral. In the event the counterparty to these transactions does not return the cash deposited, the Company may be exposed to the risk of selling the securities at prevailing market prices. The Company mitigates this risk by requiring credit approvals for counterparties, by monitoring the collateral values on a daily basis and requiring collateral to be returned by the counterparties when necessary, and by participating in a risk-sharing program offered through the OCC. The Company transacts in reverse repurchase agreements (securities purchased under agreements to resell) in connection with its broker-dealer business. The Company's policy is to take possession or control of securities with a market value in excess of the principal amount loaned, plus accrued interest, in order to collateralize resale agreements. The Company monitors the market value of the underlying securities that collateralize the related receivable on resale agreements on a daily basis and may require additional collateral when deemed appropriate. The Company utilizes securities sold under agreements to repurchase (repurchase agreements) to finance its short-term liquidity and capital needs. Under these agreements, the Company receives cash from the counterparties and provides U.S. Treasury securities as collateral, allowing the counterparties the right to sell or repledge the collateral. These agreements expose the Company to credit losses in the event the counterparties cannot meet their obligations. The Company mitigates this risk by requiring credit approvals for counterparties, by monitoring the market value of pledged securities owned on a daily basis and requiring the counterparties to return cash or excess collateral pledged when necessary. The Company has accepted collateral in connection with client margin loans and securities borrowed. Under applicable agreements, the Company is generally permitted to repledge securities held as collateral and use them to enter into securities lending arrangements. The following table summarizes the fair values of client margin securities and stock borrowings that were available to the Company to utilize as collateral on various borrowings or for other purposes, and the amount of that collateral loaned or repledged by the Company (dollars in billions): September 30, 2018 2017 Client margin securities $ 31.4 $ 23.8 Stock borrowings 0.8 1.2 Total collateral available $ 32.2 $ 25.0 Collateral loaned $ 2.9 $ 2.4 Collateral repledged 6.3 4.1 Total collateral loaned or repledged $ 9.2 $ 6.5 The Company is subject to cash deposit and collateral requirements with clearinghouses based on its clients' trading activity. The following table summarizes cash deposited with and securities pledged to clearinghouses by the Company (dollars in millions): September 30, Assets Balance Sheet Classification 2018 2017 Cash Receivable from brokers, dealers and clearing organizations $ 545 $ 151 U.S. government debt securities Securities owned, at fair value 50 398 Total $ 595 $ 549 The Company enters into off-balance sheet arrangements with TD and unaffiliated third-party depository financial institutions (together, the "Sweep Program Counterparties") to manage its sweep program. The sweep program is offered to eligible clients whereby the client's uninvested cash is swept into FDIC-insured (up to specified limits) money market deposit accounts at the Sweep Program Counterparties. The Company earns revenue on client cash at the Sweep Program Counterparties based on the return of floating-rate and fixed-rate notional investments. The Company designates amounts and maturity dates for the fixed-rate notional investments within the sweep program portfolios, subject to certain limitations. In the event the Company instructs the Sweep Program Counterparties to withdraw a fixed-rate notional investment prior to its maturity, the Company may be required to reimburse the Sweep Program Counterparties for any losses as a result of the early withdrawal. In order to mitigate the risk of potential loss due to the early withdrawal of fixed-rate notional investments, the Company maintains a certain level of short-term floating-rate investments within the sweep program portfolios to meet client cash demands. See " Insured Deposit Account Agreement " in Note 21 for a description of the sweep arrangement between the Company and TD. Guarantees The Company is a member of and provides guarantees to securities clearinghouses and exchanges in connection with client trading activities. Under related agreements, the Company is generally required to guarantee the performance of other members. Under these agreements, if a member becomes unable to satisfy its obligations to the clearinghouse, other members would be required to meet shortfalls. The Company's liability under these arrangements is not quantifiable and could exceed the cash and securities it has posted to the clearinghouse as collateral. However, the potential for the Company to be required to make payments under these agreements is considered remote. Accordingly, no contingent liability is carried on the Consolidated Balance Sheets for these guarantees. The Company clears its clients' futures transactions on an omnibus account basis through unaffiliated clearing firms. The Company also contracts with an external provider to facilitate foreign exchange trading for its clients. The Company has agreed to indemnify these unaffiliated clearing firms and the external provider for any loss that they may incur from the client transactions introduced to them by the Company. See " Insured Deposit Account Agreement " in Note 21 for a description of the guarantees included in that agreement.

Fair Value Disclosures

Fair Value Disclosures	12 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Disclosures	Fair Value Disclosures Fair Value Measurement — Definition and Hierarchy ASC 820-10, Fair Value Measurement , defines fair value as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. ASC 820-10 establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs reflect the assumptions market participants would use in pricing the asset or liability, developed based on market data obtained from sources independent of the Company. Unobservable inputs reflect the Company's own assumptions about the assumptions market participants would use in pricing the asset or liability, developed based on the best information available in the circumstances. The fair value hierarchy prioritizes the inputs to valuation techniques used to measure fair value into three broad levels, as follows: • Level 1 — Quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access. This category includes active exchange-traded funds, money market mutual funds, mutual funds and equity securities. • Level 2 — Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, either directly or indirectly. Such inputs include quoted prices in markets that are not active, quoted prices for similar assets and liabilities in active and inactive markets, inputs other than quoted prices that are observable for the asset or liability and inputs that are derived principally from or corroborated by observable market data by correlation or other means. This category includes most debt securities, U.S. government agency mortgage-backed securities, which consist of Ginnie Mae Home Equity Conversion Mortgages, and other interest-sensitive financial instruments. • Level 3 — Unobservable inputs for the asset or liability, where there is little, if any, observable market activity or data for the asset or liability. The following tables present the Company's fair value hierarchy for assets and liabilities measured at fair value on a recurring basis as of September 30, 2018 and 2017 (dollars in millions): As of September 30, 2018 Level 1 Level 2 Level 3 Fair Value Assets: Cash equivalents: Money market mutual funds $ 2,373 $ — $ — $ 2,373 Investments segregated and on deposit for regulatory purposes: U.S. government debt securities — 225 — 225 U.S. government agency mortgage-backed securities — 1,302 — 1,302 Subtotal - Investments segregated for regulatory purposes — 1,527 — 1,527 Securities owned: U.S. government debt securities — 149 — 149 Other 1 6 — 7 Subtotal - Securities owned 1 155 — 156 Investments available-for-sale: U.S. government debt securities — 484 — 484 Other assets: Pay-variable interest rate swaps (1) — 2 — 2 U.S. government debt securities — 1 — 1 Auction rate securities — — 1 1 Subtotal - Other assets — 3 1 4 Total assets at fair value $ 2,374 $ 2,169 $ 1 $ 4,544 Liabilities: Accounts payable and other liabilities: Pay-variable interest rate swaps (1) $ — $ 96 $ — $ 96 (1) See " Fair Value Hedging " in Note 10 for details. As of September 30, 2017 Level 1 Level 2 Level 3 Fair Value Assets: Cash equivalents: Money market mutual funds $ 1,081 $ — $ — $ 1,081 Investments segregated and on deposit for regulatory purposes: U.S. government debt securities — 4,094 — 4,094 U.S. government agency mortgage-backed securities — 1,486 — 1,486 Subtotal - Investments segregated for regulatory purposes — 5,580 — 5,580 Securities owned: U.S. government debt securities — 498 — 498 Other 1 4 — 5 Subtotal - Securities owned 1 502 — 503 Investments available-for-sale: U.S. government debt securities — 746 — 746 Other assets: Pay-variable interest rate swaps (1) — 26 — 26 U.S. government debt securities — 1 — 1 Auction rate securities — — 1 1 Subtotal - Other assets — 27 1 28 Total assets at fair value $ 1,082 $ 6,855 $ 1 $ 7,938 Liabilities: Accounts payable and other liabilities: Pay-variable interest rate swaps (1) $ — $ 3 $ — $ 3 (1) See " Fair Value Hedging " in Note 10 for details. There were no transfers between any levels of the fair value hierarchy during the periods covered by this report. Valuation Techniques In general, and where applicable, the Company uses quoted prices in active markets for identical assets or liabilities to determine fair value. This pricing methodology applies to the Company's Level 1 assets and liabilities. If quoted prices in active markets for identical assets and liabilities are not available to determine fair value, then the Company uses quoted prices for similar assets and liabilities or inputs other than the quoted prices that are observable, either directly or indirectly. This pricing methodology applies to the Company's Level 2 assets and liabilities. Level 2 Measurements: Debt securities — Fair values for debt securities are based on prices obtained from an independent pricing vendor. The primary inputs to the valuation include quoted prices for similar assets in active markets, quoted prices for identical or similar assets in markets that are not active, contractual cash flows, benchmark yields and credit spreads. The Company validates the vendor pricing by periodically comparing it to pricing from another independent pricing service. The Company has not adjusted prices obtained from the independent pricing vendor for any periods presented in the consolidated financial statements because no significant pricing differences have been observed. U.S. government agency mortgage-backed securities — Fair values for mortgage-backed securities are based on prices obtained from an independent pricing vendor. The primary inputs to the valuation include quoted prices for similar assets in active markets and in markets that are not active, a market-derived prepayment curve, weighted average yields on the underlying collateral and spreads to benchmark indices. The Company validates the vendor pricing by periodically comparing it to pricing from two other independent sources. The Company has not adjusted prices obtained from the independent pricing vendor for any periods presented in the consolidated financial statements because no significant pricing differences have been observed. Interest rate swaps — These derivatives are valued by the Company using a valuation model provided by a third-party service that incorporates interest rate yield curves, which are observable for substantially the full term of the contract. The valuation model is widely accepted in the financial services industry and does not involve significant judgment because most of the inputs are observable in the marketplace. Credit risk is not an input to the valuation because in each case the Company or counterparty has possession of collateral, in the form of cash or U.S. Treasury securities, in amounts equal to or exceeding the fair value of the interest rate swaps. The Company validates the third-party service valuations by comparing them to valuation models provided by the swap counterparties. Level 3 Measurements: The Company has no material assets or liabilities classified as Level 3 of the fair value hierarchy. Fair Value of Financial Instruments Not Recorded at Fair Value Receivable from/payable to brokers, dealers and clearing organizations, receivable from/payable to clients, receivable from/payable to affiliates, other receivables, accounts payable and other liabilities and certain other borrowings are short-term in nature and accordingly are carried at amounts that approximate fair value. These financial instruments are recorded at or near their respective transaction prices and historically have been settled or converted to cash at approximately that value (categorized as Level 2 of the fair value hierarchy). Cash and investments segregated and on deposit for regulatory purposes and other assets include reverse repurchase agreements (securities purchased under agreements to resell). Reverse repurchase agreements are treated as collateralized financing transactions and are carried at amounts at which the securities will subsequently be resold, plus accrued interest. The Company's reverse repurchase agreements generally have a maturity of seven days and are collateralized by securities in amounts exceeding the carrying value of the resale agreements. Accordingly, the carrying value of reverse repurchase agreements approximates fair value (categorized as Level 2 of the fair value hierarchy). Cash and investments segregated and on deposit for regulatory purposes also includes cash held in demand deposit accounts and on deposit with futures commission merchants, for which the carrying values approximate the fair value (categorized as Level 1 of the fair value hierarchy). See Note 4 for a summary of cash and investments segregated and on deposit for regulatory purposes. Other assets included reverse repurchase agreements of $65 million as of September 30, 2017. Securities sold under agreements to repurchase (repurchase agreements) — Under repurchase agreements the Company receives cash from the counterparties and provides U.S. Treasury securities as collateral. The obligations to repurchase securities sold are reflected as a liability on the Consolidated Balance Sheets. Repurchase agreements are treated as collateralized financing transactions and are carried at amounts at which the securities will subsequently be repurchased, plus accrued interest. The Company's repurchase agreements are short-term in nature and accordingly the carrying value is a reasonable estimate of fair value (categorized as Level 2 of the fair value hierarchy). Long-term debt — As of September 30, 2018 , the Company's Senior Notes had an aggregate estimated fair value, based on quoted market prices (categorized as Level 1 of the fair value hierarchy), of approximately $2.51 billion , compared to the aggregate carrying value of the Senior Notes on the Consolidated Balance Sheet of $2.44 billion . As of September 30, 2017 , the Company's Senior Notes had an aggregate estimated fair value, based on quoted market prices, of approximately $2.63 billion , compared to the aggregate carrying value of the Senior Notes on the Consolidated Balance Sheet of $2.56 billion .

Offsetting Assets and Liabiliti

Offsetting Assets and Liabilities	12 Months Ended
	Sep. 30, 2018
Offsetting [Abstract]
Offsetting Assets and Liabilities	Offsetting Assets and Liabilities Substantially all of the Company's securities sold under agreements to repurchase (repurchase agreements), reverse repurchase agreements, securities borrowing and securities lending activity and derivative financial instruments are transacted under master agreements that may allow for net settlement in the ordinary course of business, as well as offsetting of all contracts with a given counterparty in the event of default by one of the parties. However, for financial statement purposes, the Company does not net balances related to these financial instruments. The following tables present information about the potential effect of rights of setoff associated with the Company's recognized assets and liabilities as of September 30, 2018 and 2017 (dollars in millions): September 30, 2018 Gross Amounts Not Offset in the Consolidated Balance Sheet Gross Amounts of Recognized Assets and Liabilities Gross Amounts Offset in the Consolidated Balance Sheet Net Amounts Presented in the Consolidated Balance Sheet Financial Instruments (5) Collateral Received or Pledged (Including Cash) (6) Net Amount (7) Assets: Investments segregated for regulatory purposes: Reverse repurchase agreements $ 500 $ — $ 500 $ — $ (500 ) $ — Receivable from brokers, dealers and clearing organizations: Deposits paid for securities borrowed (1) 803 — 803 (41 ) (744 ) 18 Other assets: Pay-variable interest rate swaps 2 — 2 (2 ) — — Total $ 1,305 $ — $ 1,305 $ (43 ) $ (1,244 ) $ 18 Liabilities: Payable to brokers, dealers and clearing organizations: Deposits received for securities loaned (2)(3) $ 2,914 $ — $ 2,914 $ (43 ) $ (2,544 ) $ 327 Securities sold under agreements to repurchase (4) 96 — 96 (96 ) — — Accounts payable and other liabilities: Pay-variable interest rate swaps 96 — 96 (82 ) — 14 Total $ 3,106 $ — $ 3,106 $ (221 ) $ (2,544 ) $ 341 September 30, 2017 Gross Amounts Not Offset in the Consolidated Balance Sheet Gross Amounts of Recognized Assets and Liabilities Gross Amounts Offset in the Consolidated Balance Sheet Net Amounts Presented in the Consolidated Balance Sheet Financial Instruments (5) Collateral Received or Pledged (Including Cash) (6) Net Amount (7) Assets: Investments segregated for regulatory purposes: Reverse repurchase agreements $ 1,004 $ — $ 1,004 $ — $ (1,004 ) $ — Receivable from brokers, dealers and clearing organizations: Deposits paid for securities borrowed (1) 1,154 — 1,154 (110 ) (1,023 ) 21 Other assets: Pay-variable interest rate swaps 26 — 26 (26 ) — — Reverse repurchase agreements 65 — 65 — (65 ) — Total other assets 91 — 91 (26 ) (65 ) — Total $ 2,249 $ — $ 2,249 $ (136 ) $ (2,092 ) $ 21 Liabilities: Payable to brokers, dealers and clearing organizations: Deposits received for securities loaned (2)(3) $ 2,449 $ — $ 2,449 $ (112 ) $ (2,113 ) $ 224 Securities sold under agreements to repurchase (4) 97 — 97 (97 ) — — Accounts payable and other liabilities: Pay-variable interest rate swaps 3 — 3 (1 ) — 2 Total $ 2,549 $ — $ 2,549 $ (210 ) $ (2,113 ) $ 226 (1) Included in the gross amounts of deposits paid for securities borrowed is $462 million and $675 million as of September 30, 2018 and 2017 , respectively, transacted through a risk-sharing program with the OCC, which guarantees the return of cash to the Company. See " General Contingencies " in Note 15 for a discussion of the potential risks associated with securities borrowing transactions and how the Company mitigates those risks. (2) Included in the gross amounts of deposits received for securities loaned is $2.01 billion and $1.65 billion as of September 30, 2018 and 2017 , respectively, transacted through a risk-sharing program with the OCC, which guarantees the return of securities to the Company. See " General Contingencies " in Note 15 for a discussion of the potential risks associated with securities lending transactions and how the Company mitigates those risks. (3) Substantially all of the Company's securities lending transactions have a continuous contractual term and, upon notice by either party, may be terminated within two business days. The following table summarizes the Company's gross liability for securities lending transactions by the class of securities loaned (dollars in millions): September 30, 2018 2017 Deposits received for securities loaned: Equity securities $ 2,583 $ 2,109 Exchange-traded funds 223 230 Closed-end funds 74 66 Other 34 44 Total $ 2,914 $ 2,449 (4) The collateral pledged includes available-for-sale U.S. government debt securities at fair value. All of the Company's repurchase agreements have a remaining contractual maturity of less than 90 days and, upon default by either party, may be terminated at the option of the non-defaulting party. See " General Contingencies " in Note 15 for a discussion of the potential risks associated with repurchase agreements and how the Company mitigates those risks. (5) Amounts represent recognized assets and liabilities that are subject to enforceable master agreements with rights of setoff. (6) Represents the fair value of collateral the Company had received or pledged under enforceable master agreements, limited for table presentation purposes to the net amount of the recognized assets due from or liabilities due to each counterparty. At September 30, 2018 and 2017 , the Company had received total collateral with a fair value of $1.30 billion and $2.26 billion , respectively, and pledged total collateral with a fair value of $2.76 billion and $2.32 billion , respectively. (7) Represents the amount for which, in the case of net recognized assets, the Company had not received collateral, and in the case of net recognized liabilities, the Company had not pledged collateral.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	12 Months Ended
	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss The following table presents the net change in fair value recorded for each component of other comprehensive income (loss) before and after income tax for the fiscal years indicated (dollars in millions): 2018 2017 2016 Before Tax Tax Effect Net of Tax Before Tax Tax Effect Net of Tax Before Tax Tax Effect Net of Tax Investments available-for-sale: Unrealized loss $ (12 ) $ 3 $ (9 ) $ (9 ) $ 4 $ (5 ) $ — $ — $ — Reclassification adjustment for realized loss included in net income (1) 11 (4 ) 7 — — — — — — Net change in investments available-for-sale (1 ) (1 ) (2 ) (9 ) 4 (5 ) — — — Cash flow hedging instruments: Reclassification adjustment for portion of realized loss amortized to net income (2) 5 (1 ) 4 4 (2 ) 2 5 (2 ) 3 Net change in cash flow hedging instruments 5 (1 ) 4 4 (2 ) 2 5 (2 ) 3 Other comprehensive income (loss) $ 4 $ (2 ) $ 2 $ (5 ) $ 2 $ (3 ) $ 5 $ (2 ) $ 3 (1) The before tax reclassification amount and related tax effect are included in loss on sale of investments and provision for income taxes, respectively, on the Consolidated Statements of Income. (2) The before tax reclassification amounts and the related tax effects are included in interest on borrowings and provision for income taxes, respectively, on the Consolidated Statements of Income. The following table presents after-tax changes in each component of accumulated other comprehensive loss for the fiscal years indicated (dollars in millions): 2018 2017 2016 Investments available-for-sale: Beginning balance $ (5 ) $ — $ — Other comprehensive loss before reclassification (9 ) (5 ) — Amount reclassified from accumulated other comprehensive loss 7 — — Current period change (2 ) (5 ) — Ending balance $ (7 ) $ (5 ) $ — Cash flow hedging instruments: Beginning balance $ (20 ) $ (22 ) $ (25 ) Amount reclassified from accumulated other comprehensive loss 4 2 3 Adoption of Accounting Standards Update 2018-02 (Note 1) (4 ) — — Current period change — 2 3 Ending balance $ (20 ) $ (20 ) $ (22 ) Total accumulated other comprehensive loss: Beginning balance $ (25 ) $ (22 ) $ (25 ) Current period change (2 ) (3 ) 3 Ending balance $ (27 ) $ (25 ) $ (22 )

Segment and Geographic Area Inf

Segment and Geographic Area Information	12 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Segment and Geographic Area Information	Segment and Geographic Area Information The Company primarily operates in the securities brokerage industry and has no other reportable segments. Substantially all of the Company's revenues from external clients for the fiscal years ended September 30, 2018 , 2017 and 2016 were derived from its operations in the United States.

Accelerated Stock Repurchase Ag

Accelerated Stock Repurchase Agreements	12 Months Ended
	Sep. 30, 2018
Accelerated Stock Repurchase [Abstract]
Accelerated Stock Repurchase Agreements	Accelerated Stock Repurchase Agreements On September 12, 2018, the Company entered into an agreement with an investment bank counterparty to purchase shares of its common stock under an accelerated stock repurchase transaction (the "September 2018 ASR Agreement"). The Company paid $150 million to the counterparty and received an initial delivery of 2.2 million shares of its common stock on September 13, 2018, representing 80% of the potential shares to be repurchased based on the closing stock price of $54.69 on September 12, 2018. Settlement of the transaction occurred after the end of an averaging period, which began on September 13, 2018 and ended on October 12, 2018. The total number of shares the Company purchased from the counterparty was based on the average of the daily volume-weighted average share prices of the Company's common stock during the averaging period, less a pre-determined discount. Upon settlement, the Company received an additional 0.6 million shares on October 16, 2018. The Company ultimately repurchased a total of approximately 2.8 million shares under the September 2018 ASR Agreement at a net weighted average price of $53.13 per share. In June 2016, the Company entered into an agreement with an investment bank counterparty to purchase $42.5 million of its common stock under an accelerated stock repurchase transaction (the "June 2016 ASR Agreement"). Pursuant to the terms of the June 2016 ASR Agreement, the Company received an initial delivery of 1.1 million shares of its common stock in June 2016 and received an additional 0.3 million shares upon completion of the agreement in September 2016. The Company ultimately repurchased a total of approximately 1.4 million shares under the June 2016 ASR Agreement at a net weighted average price of $29.89 per share. In December 2015, the Company entered into an agreement with an investment bank counterparty to purchase $45 million of its common stock under an accelerated stock repurchase transaction (the "December 2015 ASR Agreement"). Pursuant to the terms of the December 2015 ASR Agreement, the Company received an initial delivery of 1.0 million shares of its common stock in December 2015 and received an additional 0.3 million shares upon completion of the agreement in January 2016. The Company ultimately repurchased a total of approximately 1.3 million shares under the December 2015 ASR Agreement at a net weighted average price of $33.98 per share. The Company treated the ASR agreements as forward contracts indexed to its own common stock. The forward contracts met all of the applicable criteria for equity classification, including the Company's right to settle in shares. The Company reflected the shares received from the investment bank counterparties as treasury stock as of the dates the shares were delivered, which resulted in reductions of the outstanding shares used to calculate the weighted average common shares outstanding for both basic and diluted earnings per share during the respective periods.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions Transactions with TD and its Affiliates As a result of the Company's acquisition of TD Waterhouse Group, Inc. during fiscal year 2006, TD became an affiliate of the Company. TD owned approximately 42% of the Company's common stock as of September 30, 2018 . Pursuant to the stockholders agreement between TD and the Company, TD has the right to designate five of twelve members of the Company's board of directors. The Company transacts business and has extensive relationships with TD and certain of its affiliates. Transactions with TD and its affiliates are discussed and summarized below. Insured Deposit Account Agreement Under the IDA agreement, TD Bank USA and TD Bank, N.A. (together, the "TD Depository Institutions") make available to clients of the Company FDIC-insured (up to specified limits) money market deposit accounts as either designated sweep vehicles or as non-sweep deposit accounts. The Company provides marketing, recordkeeping and support services for the TD Depository Institutions with respect to the money market deposit accounts. In exchange for providing these services, the TD Depository Institutions pay the Company an aggregate marketing fee based on the weighted average yield earned on the client IDA assets, less the actual interest paid to clients, a servicing fee to the TD Depository Institutions and the cost of FDIC insurance premiums. The current IDA agreement became effective as of January 1, 2013 and had an initial term expiring July 1, 2018 . It is automatically renewable for successive five -year terms, provided that it may be terminated by either the Company or the TD Depository Institutions by providing written notice of non-renewal at least two years prior to the initial expiration date or the expiration date of any subsequent renewal period. As of July 1, 2016, notice of non-renewal was not provided by either party, therefore the IDA agreement was automatically renewed for an additional five-year term on July 1, 2018 . The fee earned on the IDA agreement is calculated based on two primary components: (a) the yield on fixed-rate notional investments, based on prevailing fixed rates for identical balances and maturities in the interest rate swap market (generally LIBOR-based) at the time such investments were added to the IDA portfolio (including any adjustments required to adjust the variable rate leg of such swaps to a one -month reset frequency and the overall swap payment frequency to monthly) and (b) the yield on floating-rate investments. As of September 30, 2018 , the IDA portfolio was comprised of approximately 78% fixed-rate notional investments and 22% floating-rate investments. The IDA agreement provides that the Company may designate amounts and maturity dates for the fixed-rate notional investments in the IDA portfolio, subject to certain limitations. For example, if the Company designates that $100 million of deposits be invested in 5 -year fixed-rate investments, and on the day such investment is confirmed by the TD Depository Institutions the prevailing fixed yield for the applicable 5 -year U.S. dollar LIBOR-based swaps is 1.45% , then the Company will earn a gross fixed yield of 1.45% on that portion of the portfolio (before any deductions for interest paid to clients, the servicing fee to the TD Depository Institutions and the cost of FDIC insurance premiums). In the event that (1) the federal funds effective rate is established at 0.75% or greater and (2) the rate on 5 -year U.S. dollar interest rate swaps is equal to or greater than 1.50% for 20 consecutive business days, then the rate earned by the Company on new fixed-rate notional investments will be reduced by 20% of the excess of the 5 -year U.S. dollar swap rate over 1.50% , up to a maximum of 0.10% . The yield on floating-rate investments is calculated daily based on the greater of the following rates published by the Federal Reserve: (1) the interest rate paid by Federal Reserve Banks on balances held in excess of required reserve balances and contractual clearing balances under Regulation D and (2) the daily effective federal funds rate. The interest rates paid to clients are set by the TD Depository Institutions and are not linked to any index. The servicing fee to the TD Depository Institutions under the IDA agreement is equal to 25 basis points on the aggregate average daily balance in the IDA accounts, subject to adjustment as it relates to deposits of less than or equal to $20 billion kept in floating-rate investments or in fixed-rate notional investments with a maturity of up to 24 months ("short-term fixed-rate investments"). For such floating-rate and short-term fixed-rate investments, the servicing fee is equal to the difference of the interest rate earned on the investments less the FDIC premiums paid (in basis points), divided by two. The servicing fee has a floor of 3 basis points (subject to adjustment from time to time to reflect material changes to the TD Depository Institutions' leverage costs) and a maximum of 25 basis points. In the event the marketing fee computation results in a negative amount, the Company must pay the TD Depository Institutions the negative amount. This effectively results in the Company guaranteeing the TD Depository Institutions revenue equal to the servicing fee on the IDA agreement, plus the reimbursement of FDIC insurance premiums. The marketing fee computation under the IDA agreement is affected by many variables, including the type, duration, principal balance and yield of the fixed-rate and floating-rate investments, the prevailing interest rate environment, the amount of client deposits and the yield paid on client deposits. Because a negative marketing fee computation would arise only if there were extraordinary movements in many of these variables, the maximum potential amount of future payments the Company could be required to make under this arrangement cannot be reasonably estimated. Management believes the likelihood that the marketing fee calculation would result in a negative amount is remote. Accordingly, no contingent liability is carried on the Consolidated Balance Sheets for the IDA agreement. In the event the Company withdraws a notional investment prior to its maturity, the Company is required to reimburse the TD Depository Institutions an amount equal to the economic replacement value of the investment, as defined in the IDA agreement. See "General Contingencies" in Note 15 for a discussion of how the Company mitigates the risk of losses due to the early withdrawal of fixed-rate notional investments. In addition, the Company has various other services agreements and transactions with TD and its affiliates. The following tables summarize revenues and expenses resulting from transactions with TD and its affiliates for the fiscal years indicated (dollars in millions): Description Statement of Income Classification Revenues from TD and its Affiliates 2018 2017 2016 Insured Deposit Account Agreement Bank deposit account fees $ 1,426 $ 1,101 $ 926 Mutual Fund Agreements Investment product fees 17 15 11 Other Various 13 10 7 Total revenues $ 1,456 $ 1,126 $ 944 Description Statement of Income Classification Expenses to TD and its Affiliates 2018 2017 2016 Canadian Call Center Services Agreement (1) Various $ — $ 11 $ 22 Referral and Strategic Alliance Agreement Other expense 5 5 3 Other Various 2 1 1 Total expenses $ 7 $ 17 $ 26 (1) The Company notified TD of its intent to not extend or renew the Canadian Call Center Services Agreement and services under this agreement ended by September 30, 2017 . The following table summarizes the classification and amount of receivables from and payables to TD and its affiliates on the Consolidated Balance Sheets resulting from related party transactions (dollars in millions): September 30, 2018 2017 Assets: Receivable from affiliates $ 151 $ 110 Liabilities: Payable to brokers, dealers and clearing organizations $ 47 $ 37 Payable to affiliates 7 38 Payables to brokers, dealers and clearing organizations primarily relate to securities lending activity and are settled in accordance with customary contractual terms. Receivables from and payables to TD affiliates resulting from client cash sweep activity are generally settled in cash the next business day. Other receivables from and payables to affiliates of TD are generally settled in cash on a monthly basis. As of September 30, 2018, payables to affiliates on the Consolidated Balance Sheets included $38 million of liabilities assumed in connection with the acquisition of Scottrade. These liabilities were settled during the first quarter of fiscal year 2019. As of September 30, 2017, receivables from and payables to affiliates included $27 million of assets acquired and $71 million of liabilities assumed, respectively, in connection with the acquisition of Scottrade.

Condensed Financial Information

Condensed Financial Information (Parent Company Only)	12 Months Ended
	Sep. 30, 2018
Condensed Financial Information Disclosure [Abstract]
Condensed Financial Information (Parent Company Only)	Condensed Financial Information (Parent Company Only) The following tables present the Parent company's condensed balance sheets, statements of income and statements of cash flows. Because all other comprehensive income (loss) activity occurred on the Parent company for all periods presented, the Parent company's condensed statements of comprehensive income are not presented. PARENT COMPANY ONLY CONDENSED BALANCE SHEETS As of September 30, 2018 and 2017 2018 2017 (In millions) ASSETS Cash and cash equivalents $ 151 $ 154 Receivable from subsidiaries 8 6 Investments available-for-sale, at fair value (including $98 million and $99 million of securities pledged as collateral for repurchase agreements at September 30, 2018 and 2017, respectively) 484 746 Investments in subsidiaries 9,976 9,043 Other, net 162 108 Total assets $ 10,781 $ 10,057 LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities: Accounts payable and other liabilities $ 240 $ 104 Payable to subsidiaries and affiliates 3 54 Securities sold under agreements to repurchase 96 97 Long-term debt 2,439 2,555 Total liabilities 2,778 2,810 Stockholders' equity 8,003 7,247 Total liabilities and stockholders' equity $ 10,781 $ 10,057 PARENT COMPANY ONLY CONDENSED STATEMENTS OF INCOME For the Years Ended September 30, 2018 , 2017 and 2016 2018 2017 2016 (In millions) Net revenues $ 52 $ 31 $ 30 Operating expenses 21 34 26 Operating income (loss) 31 (3 ) 4 Other expense 106 71 53 Loss before income taxes and equity in income of subsidiaries (75 ) (74 ) (49 ) Provision for (benefit from) income taxes 15 (22 ) 6 Loss before equity in income of subsidiaries (90 ) (52 ) (55 ) Equity in income of subsidiaries 1,563 924 897 Net income $ 1,473 $ 872 $ 842 PARENT COMPANY ONLY CONDENSED STATEMENTS OF CASH FLOWS For the Years Ended September 30, 2018 , 2017 and 2016 2018 2017 2016 (In millions) Cash flows from operating activities: Net income $ 1,473 $ 872 $ 842 Adjustments to reconcile net income to net cash flows provided by operating activities: Equity in income of subsidiaries (1,563 ) (924 ) (897 ) Deferred income taxes 13 (12 ) — Dividends from subsidiaries 1,030 1,230 825 Loss on sale of investments 11 — — Stock-based compensation 60 36 34 Other, net 9 9 8 Changes in operating assets and liabilities: Receivable from subsidiaries (2 ) 2 (3 ) Other assets (92 ) — 1 Accounts payable and other liabilities 42 (67 ) 38 Payable to subsidiaries and affiliates (24 ) (4 ) 26 Net cash provided by operating activities 957 1,142 874 Cash flows from investing activities: Investment in subsidiaries (425 ) (15 ) (60 ) Loans made under intercompany credit agreements (175 ) — — Collections on intercompany credit agreements 175 — — Cash paid in business acquisition (4 ) (1,698 ) — Proceeds from sale of investments available-for-sale, at fair value 643 — — Purchase of investments available-for-sale, at fair value (392 ) — (757 ) Proceeds from sale and maturity of short-term investments — — 600 Purchase of short-term investments — — (601 ) Net cash used in investing activities (178 ) (1,713 ) (818 ) Cash flows from financing activities: Proceeds from issuance of long-term debt — 798 — Payment of debt issuance costs (3 ) (8 ) — Principal payments on long-term debt — (385 ) — Reimbursement (payment) of prepayment premium on long-term debt 2 (54 ) — Net proceeds from (payments on) securities sold under agreements to repurchase (1 ) 97 — Proceeds from Parent Senior Revolving Facility 200 — — Principal payments on Parent Senior Revolving Facility (200 ) — — Payment of cash dividends (477 ) (379 ) (362 ) Proceeds from issuance of common stock — 400 — Purchase of treasury stock (255 ) — (352 ) Purchase of treasury stock for income tax withholding on stock-based compensation (17 ) (27 ) (30 ) Payment for future treasury stock under accelerated stock repurchase agreement (31 ) — — Other, net — 35 16 Net cash provided by (used in) financing activities (782 ) 477 (728 ) Net decrease in cash and cash equivalents (3 ) (94 ) (672 ) Cash and cash equivalents at beginning of year 154 248 920 Cash and cash equivalents at end of year $ 151 $ 154 $ 248 Supplemental cash flow information: Interest paid $ 94 $ 50 $ 47 Income taxes paid $ 309 $ 452 $ 488 Noncash investing activities: Issuance of common stock in acquisition $ — $ 1,261 $ — Assets transferred to a subsidiary, net $ — $ 15 $ —

Quarterly Data (Unaudited)

Quarterly Data (Unaudited)	12 Months Ended
	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Data (Unaudited)	Quarterly Data (Unaudited) (Dollars in millions, except per share amounts) For the Fiscal Year Ended September 30, 2018 First Quarter Second Quarter Third Fourth Net revenues $ 1,257 $ 1,415 $ 1,382 $ 1,398 Operating income $ 336 $ 396 $ 631 $ 635 Net income $ 297 $ 271 $ 451 $ 454 Basic earnings per share $ 0.52 $ 0.48 $ 0.79 $ 0.80 Diluted earnings per share $ 0.52 $ 0.48 $ 0.79 $ 0.80 For the Fiscal Year Ended September 30, 2017 First Quarter Second Quarter Third Quarter Fourth Net revenues $ 859 $ 904 $ 931 $ 983 Operating income $ 353 $ 358 $ 394 $ 361 Net income $ 216 $ 214 $ 231 $ 211 Basic earnings per share $ 0.41 $ 0.41 $ 0.44 $ 0.40 Diluted earnings per share $ 0.41 $ 0.40 $ 0.44 $ 0.39 Quarterly amounts may not sum to fiscal year totals due to rounding.

Subsequent Event

Subsequent Event	12 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event Senior Notes — On October 30, 2018, the Company sold, through a public offering, $600 million aggregate principal amount of unsecured variable-rate senior notes due November 1, 2021 (the "2021 Notes") and $400 million aggregate principal amount of unsecured 3.750% senior notes due April 1, 2024 (the "2024 Notes"). The Company intends to use the net proceeds from the issuance of the 2021 Notes and 2024 Notes for general corporate purposes, including to augment liquidity. The 2021 Notes will bear interest at a variable rate, reset quarterly, equal to three-month LIBOR plus 0.430% per annum, payable quarterly on February 1, May 1, August 1 and November 1 of each year, beginning on February 1, 2019. Interest on the fixed-rate 2024 Notes will be payable in arrears semi-annually on April 1 and October 1 of each year, beginning on April 1, 2019. The Company's obligations in respect to the 2021 Notes and the 2024 Notes are not guaranteed by any of its subsidiaries. The Company may redeem the 2024 Notes, in whole or in part, at any time prior to March 2, 2024 at a redemption price equal to the greater of (a) 100% of the principal amount of the notes being redeemed, and (b) the sum of the present values of the remaining scheduled payments of principal and interest on the notes being redeemed, discounted to the date of redemption on a semi-annual basis at the comparable U.S. Treasury rate, plus 15 basis points, plus accrued and unpaid interest to the date of redemption. The Company may redeem the 2021 Notes and 2024 Notes, in whole or in part, at any time on or after October 2, 2021 and March 2, 2024, respectively, at a redemption price equal to 100% of the principal amount of the notes being redeemed, plus, in each case, accrued and unpaid interest to the date of redemption.

Nature of Operations and Summ_2

Nature of Operations and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation — The consolidated financial statements include the accounts of TD Ameritrade Holding Corporation (the "Parent"), a Delaware corporation, and its wholly-owned subsidiaries (collectively, the "Company"). Intercompany balances and transactions have been eliminated.
Nature of Operations	Nature of Operations — The Company provides securities brokerage services, including trade execution, clearing services and margin lending, through its broker-dealer subsidiaries; futures and foreign exchange trade execution services through its futures commission merchant ("FCM") and forex dealer member ("FDM") subsidiary; and trustee, custodial and other trust-related services to retirement plans and other custodial accounts through its state-chartered trust company subsidiary. The Company also provides cash sweep and deposit account products through third-party relationships, including relationships with affiliates. The Company's broker-dealer subsidiaries are subject to regulation by the Securities and Exchange Commission ("SEC"), the Financial Industry Regulatory Authority ("FINRA") and the various exchanges in which they maintain membership. The Company's FCM/FDM subsidiary is subject to regulation by the Commodity Futures Trading Commission ("CFTC") and the National Futures Association ("NFA"). Dividends from the Company's broker-dealer, FCM/FDM and trust company subsidiaries are a source of liquidity for the Parent. Requirements of the SEC, FINRA and CFTC relating to liquidity, net capital standards and the use of client funds and securities may limit funds available for the payment of dividends from the broker-dealer and FCM/FDM subsidiaries to the holding company. State regulatory requirements may limit funds available for the payment of dividends from the trust company subsidiary to the holding company.
Use of Estimates	Use of Estimates — The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles ("GAAP") requires management to make estimates and assumptions that affect the reported amount of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents — The Company considers temporary, highly-liquid investments with an original maturity of three months or less to be cash equivalents, except for amounts required to be segregated for regulatory purposes.
Cash and Investments Segregated and on Deposit for Regulatory Purposes	Cash and Investments Segregated and on Deposit for Regulatory Purposes — Cash and investments segregated and on deposit for regulatory purposes consists primarily of qualified deposits in special reserve bank accounts for the exclusive benefit of clients under Rule 15c3-3 of the Securities Exchange Act of 1934 (the "Exchange Act") and other regulations. Funds can be held in cash, reverse repurchase agreements, U.S. Treasury securities, U.S. government agency mortgage-backed securities and other qualified securities. Reverse repurchase agreements (securities purchased under agreements to resell) are treated as collateralized financing transactions and are carried at amounts at which the securities will subsequently be resold, plus accrued interest. The Company's reverse repurchase agreements are collateralized by U.S. government debt securities and generally have a maturity of seven days. Cash and investments segregated and on deposit for regulatory purposes also includes amounts that have been segregated or secured for the benefit of futures clients according to the regulations of the CFTC governing futures commission merchants.
Securities Borrowed and Securities Loaned	Securities Borrowed and Securities Loaned — Securities borrowed and securities loaned transactions are recorded at the amount of cash collateral provided or received. Securities borrowed transactions require the Company to provide the counterparty with collateral in the form of cash. The Company receives collateral in the form of cash for securities loaned transactions. For these transactions, the fees earned or incurred by the Company are recorded as net interest revenue on the Consolidated Statements of Income. The related interest receivable from and the brokerage interest payable to broker-dealers are included in other receivables and in accounts payable and other liabilities, respectively, on the Consolidated Balance Sheets.
Receivable from/Payable to Clients	Receivable from/Payable to Clients — Receivable from clients primarily consists of margin loans to securities brokerage clients, which are collateralized by client securities, and is carried at the amount receivable, net of an allowance for doubtful accounts that is primarily based on the amount of unsecured margin balances. Payable to clients primarily consists of client cash held in brokerage accounts and is carried at the amount of client cash on deposit. The Company earns interest revenue and pays interest expense on its receivable from client and payable to client balances, respectively. The interest revenue and expense are included in net interest revenue on the Consolidated Statements of Income.
Securities Owned	Securities Owned — Securities owned by our broker-dealer subsidiaries are recorded on a trade-date basis and carried at fair value, and the related changes in fair value are generally included in other revenues on the Consolidated Statements of Income.
Investments Available-for-sale	Investments Available-for-sale — Investments available-for-sale are carried at fair value and unrealized gains and losses, net of deferred income taxes, are reflected as a component of accumulated other comprehensive income (loss) on the Consolidated Balance Sheets. Realized gains and losses on investments available-for-sale are determined on the specific identification method and are reflected on the Consolidated Statements of Income. As of September 30, 2018 , investments available-for-sale consists of U.S. government debt securities with remaining contractual maturities between less than one year and six years. There were no material unrealized gains or losses on investments available-for-sale as of September 30, 2018 and 2017 .
Property and Equipment	Property and Equipment — Property and equipment is recorded at cost, net of accumulated depreciation and amortization, except for land, which is recorded at cost. Depreciation is provided using the straight-line method over the estimated useful service lives of the assets, which range from seven to 40 years for buildings and building components and three to seven years for all other depreciable property and equipment. Leasehold improvements are amortized over the lesser of the economic useful life of the improvement or the term of the lease.
Software Development	Software Development — From the date technological feasibility has been established until beta testing is complete, software development costs are capitalized and included in property and equipment. Once the product is fully functional, such costs are amortized in accordance with the Company's normal accounting policies. Software development costs that do not meet capitalization criteria are expensed as incurred.
Goodwill	Goodwill — The Company has recorded goodwill for purchase business combinations to the extent the purchase price of each completed acquisition exceeded the fair value of the net identifiable assets of the acquired company. The Company tests goodwill for impairment on an annual basis and more frequently as events occur or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. In performing the impairment tests, the Company utilizes quoted market prices of the Company's common stock to estimate the fair value of the Company as a whole. The estimated fair value is then allocated to the Company's reporting unit and is compared with the carrying value of the reporting unit. No impairment charges have resulted from the annual impairment tests.
Amortization of Acquired Intangible Assets	Amortization of Acquired Intangible Assets — Acquired intangible assets with finite lives are amortized on a straight-line basis over their estimated useful lives, ranging from two to 23 years. The acquired intangible asset associated with a trademark license agreement is not subject to amortization because the term of the agreement is considered to be indefinite.
Long-Lived Assets and Acquired Intangible Assets	Long-Lived Assets and Acquired Intangible Assets — The Company reviews its long-lived assets and finite-lived acquired intangible assets for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. If based on that review, changes in circumstances indicate that the carrying amount of such assets may not be recoverable, the Company evaluates recoverability by comparing the undiscounted cash flows associated with the asset to the asset's carrying amount. The Company also evaluates the remaining useful lives of intangible assets to determine if events or trends warrant a revision to the remaining period of amortization. Long-lived assets classified as "held for sale" are reported at the lesser of carrying amount or fair value less cost to sell. As of September 30, 2018 and 2017, the Company had $36 million and $5 million of assets classified as held for sale, respectively, which are included in other assets on the Consolidated Balance Sheets. The Company tests its indefinite-lived acquired intangible asset for impairment on an annual basis and more frequently as events occur or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. To determine if the indefinite-lived intangible asset is impaired, the Company first assesses certain qualitative factors. Based on this assessment, if it is determined that more likely than not the fair value of the indefinite-lived intangible asset is less than its carrying amount, the Company performs a quantitative impairment test. No impairment charges have resulted from the annual impairment tests.
Securities Sold Under Agreements to Repurchse	Securities Sold Under Agreements to Repurchase — Transactions involving sales of securities under agreements to repurchase (repurchase agreements) are treated as collateralized financing transactions. Under repurchase agreements, the Company receives cash from counterparties and provides U.S. Treasury securities as collateral. These agreements are carried at amounts at which the securities will subsequently be repurchased, plus accrued interest, and the interest expense incurred by the Company is recorded as interest on borrowings on the Consolidated Statements of Income. See " General Contingencies " in Note 15 , Commitments and Contingencies, for a discussion of the potential risks associated with repurchase agreements and how the Company mitigates those risks.
Income Taxes	Income Taxes — The Company files a consolidated U.S. income tax return with its subsidiaries on a calendar year basis, combined returns for state tax purposes where required and certain of its subsidiaries file separate state income tax returns where required. Deferred tax assets and liabilities are determined based on the differences between the financial statement carrying amounts and tax bases of assets and liabilities using enacted tax rates expected to apply to taxable income in the periods in which the deferred tax asset or liability is expected to be settled or realized. Uncertain tax positions are recognized if they are more likely than not to be sustained upon examination, based on the technical merits of the position. The amount of tax benefit recognized is the largest amount of benefit that is greater than 50% likely of being realized upon settlement. The Company recognizes interest and penalties, if any, related to income tax matters as part of the provision for income taxes on the Consolidated Statements of Income.
Capital Stock	Capital Stock — The authorized capital stock of the Company consists of a single class of common stock and one or more series of preferred stock as may be authorized for issuance by the Company's board of directors. Voting, dividend, conversion and liquidation rights of the preferred stock would be established by the board of directors upon issuance of such preferred stock.
Stock-Based Compensation	Stock-Based Compensation — The Company measures and recognizes compensation expense based on estimated grant date fair values for all stock-based payment arrangements. Stock-based compensation expense is based on awards expected to vest and therefore is reduced for estimated forfeitures. Forfeitures are estimated at the time of grant based on the Company's historical forfeiture experience and revised in subsequent periods if actual forfeitures differ from those estimates.
Deferred Compensation	Deferred Compensation — Company common stock held in a rabbi trust pursuant to a Company deferred compensation plan is recorded at the fair value of the stock at the time it is transferred to the rabbi trust and is classified as treasury stock. The corresponding deferred compensation liability is recorded as a component of stockholders' equity on the Consolidated Balance Sheets .
Revenue Recognition	Transaction-based Revenues — Client trades are recorded on a settlement-date basis with such trades generally settling within one to two business days after the trade date. Revenues and expenses related to client trades, including order routing revenue and revenues from markups on riskless principal trades in fixed-income securities, are recorded on a trade-date basis. Revenues related to client trades are recorded net of promotional allowances. Securities owned by clients, including those that collateralize margin or similar transactions, are not reflected in the accompanying consolidated financial statements. Bank Deposit Account Fees — Revenues generated from a sweep program that is offered to eligible clients of the Company whereby clients' uninvested cash is swept to FDIC-insured (up to specified limits) money market accounts at third-party financial institutions participating in the program. Bank deposit account fees includes revenues from the Insured Deposit Account ("IDA") agreement with TD Bank USA, N.A. ("TD Bank USA"), TD Bank, N.A. and The Toronto-Dominion Bank ("TD"). The IDA agreement is described further in Note 21 , Related Party Transactions. Net Interest Revenue — Net interest revenue primarily consists of income generated by interest charged to clients on margin balances, net interest revenue from securities borrowed and securities loaned transactions and interest earned on client cash, net of interest paid to clients on their credit balances. Investment Product Fees — Investment product fee revenue consists of revenues earned on client assets invested in money market mutual funds, other mutual funds and certain investment programs. Investment product fees also includes fees earned on client assets managed by independent registered investment advisors utilizing the Company's trading and investing platforms.
Advertising	Advertising — The Company expenses advertising costs the first time the advertising takes place. Client cash offers are also characterized as advertising expense, rather than as a reduction of revenue, because there is generally little or no cumulative revenue associated with an individual client earning a cash offer at the time the consideration is recognized in the Consolidated Statement of Income.
Derivatives and Hedging Activities	Derivatives and Hedging Activities — The Company occasionally utilizes derivative instruments to manage risks, which may include market price, interest rate and foreign currency risks. The Company does not use derivative instruments for speculative or trading purposes. Derivatives are recorded on the Consolidated Balance Sheets as assets or liabilities at fair value. Derivative instruments properly designated to hedge exposure to changes in the fair value of assets or liabilities are accounted for as fair value hedges. Derivative instruments properly designated to hedge exposure to the variability of expected future cash flows or other forecasted transactions are accounted for as cash flow hedges. The Company formally documents the risk management objective and strategy for each hedge transaction. Derivative instruments that do not qualify for hedge accounting are carried at fair value on the Consolidated Balance Sheets with unrealized gains and losses recorded currently on the Consolidated Statements of Income. Cash flows from derivative instruments accounted for as fair value hedges or cash flow hedges are classified in the same category on the Consolidated Statements of Cash Flows as the cash flows from the items being hedged. For additional information on the Company's fair value and cash flow hedging instruments, see Note 10 , Long-term Debt and Other Borrowings.
Earnings Per Share	Earnings Per Share — Basic earnings per share ("EPS") is computed by dividing net income by the weighted average common shares outstanding for the period. Diluted EPS reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock, except when such assumed exercise or conversion would have an antidilutive effect on EPS. The difference between the numerator and denominator used in the Company's computation of basic and diluted earnings per share consists of common stock equivalent shares related to stock-based compensation. There were no material antidilutive awards for fiscal years 2018 and 2017. The Company excluded from the calculation of diluted earnings per share 0.4 million shares underlying the stock-based compensation awards for fiscal year 2016 because their inclusion would have been antidilutive.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements ASU 2018-05 – In March 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2018-05, Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 118 . ASU 2018-05 amends Accounting Standards Codification ("ASC") 740, Income Taxes , to provide guidance on accounting for the tax effects of the Tax Cuts and Jobs Act (the "Act") pursuant to Staff Accounting Bulletin No. 118, which allows entities to complete the accounting under ASC 740 within a one-year measurement period from the Act's enactment date. This ASU was effective upon issuance. For additional information regarding the Company's accounting for the tax effects of the Act under this guidance, see Note 11, Income Taxes. ASU 2018-02 – In February 2018, the FASB issued ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income , to allow a reclassification from accumulated other comprehensive income (loss) to retained earnings for stranded income tax effects resulting from the Tax Cuts and Jobs Act enacted on December 22, 2017, and requires certain disclosures about stranded tax effects. The Company elected to early adopt the standard in the fourth quarter of fiscal year 2018, applying the updates in the period of adoption. As a result of the adoption, the Company reclassified $4 million of income tax benefits, related to cash flow hedging instruments, from accumulated other comprehensive loss to retained earnings on its Consolidated Balance Sheet. The reclassification related only to the change in the federal corporate income tax rate due to the Act. ASU 2016-09 – In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting . The guidance in ASU 2016-09 simplified several aspects of the accounting for share-based payment transactions, including: (1) recognize all excess tax benefits and tax deficiencies as income tax expense or benefit in the statement of income; (2) treat tax effects of exercised or vested awards as discrete items in the period in which they occur; (3) recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period; (4) classify excess tax benefits with other income tax cash flows as an operating activity; (5) an entity can make an accounting policy election to either estimate the number of awards that are expected to vest or account for forfeitures when they occur; (6) the threshold to qualify for equity classification will permit withholding up to the maximum statutory rates in the applicable jurisdictions; and (7) classify cash paid by an employer when directly withholding shares for tax withholding purposes as a financing activity in the statement of cash flows. The Company adopted the amended accounting guidance as of October 1, 2017, and as a result, the Company's provision for income taxes was reduced by $5 million on its Consolidated Statement of Income for the fiscal year ended September 30, 2018, due to the inclusion of excess tax benefits applied on a prospective basis. The future effects of excess tax benefits and tax deficiencies recognized in the Company's earnings will depend on the volume of equity compensation during a particular period and on the market price of the Company's common stock at the date the equity awards either vest or are exercised. In addition, the Company elected to retrospectively adopt the amendment to present excess tax benefits on share-based compensation as an operating activity on the statement of cash flows. This resulted in an increase in cash flows from operating activities and a decrease in cash flows from financing activities of $12 million and $16 million on the Company's Consolidated Statement of Cash Flows for the fiscal years ended September 30, 2017 and 2016, respectively. For the purpose of recognizing compensation cost associated with share-based awards, the Company has elected to continue to follow its current practice of estimating forfeitures. None of the other provisions in this amended guidance had a significant impact on the Company's consolidated financial statements.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements ASU 2018-13 – In August 2018, the FASB issued ASU 2018-13, Disclosure Framework–Changes to the Disclosure Requirements for Fair Value Measurement. The amendments in this standard will remove, modify and add certain disclosures under ASC Topic 820, Fair Value Measurement , with the objective of improving disclosure effectiveness. ASU 2018-13 will be effective for the Company's fiscal year beginning October 1, 2020, with early adoption permitted. The transition requirements are dependent upon each amendment within this update and will be applied either prospectively or retrospectively. Since this update is intended to modify disclosures, the adoption of ASU 2018-13 is not expected to have a material impact on the Company's consolidated financial statements. ASU 2017-12 – In August 2017, the FASB issued ASU 2017-12, Targeted Improvements to Accounting for Hedging Activities , which will amend the guidance in ASC Topic 815, Derivatives and Hedging. The objective of this ASU is to improve the financial reporting of hedging relationships to better portray the economic results of an entity's risk management activities in its financial statements through changes to both the designation and measurement guidance for qualifying hedging relationships and to the presentation of hedge results. In addition, the amendments in this ASU make certain targeted improvements to simplify the application of the hedge accounting guidance in current GAAP. All transition requirements and elections under ASU 2017-12 should be applied to hedging relationships existing on the date of adoption, with the effect of the adoption reflected as of the beginning of the fiscal year of adoption. The amended presentation and disclosure guidance is required only prospectively. ASU 2017-12 will be effective for the Company's fiscal year beginning October 1, 2019, with early adoption permitted. The Company is currently assessing the impact this ASU will have on its consolidated financial statements. ASU 2017-04 – In January 2017, the FASB issued ASU 2017-04, Simplifying the Test for Goodwill Impairment, which is intended to simplify the test for goodwill impairment by eliminating Step 2 from the goodwill impairment test, which measures a goodwill impairment loss by comparing the implied fair value of a reporting unit's goodwill with the carrying amount of that goodwill. Under the amendments in this ASU, an entity should perform its annual goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit's fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. When measuring the goodwill impairment loss, income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit should be considered, if applicable. An entity will still have the option to perform the qualitative assessment for a reporting unit to determine if the quantitative test is necessary. ASU 2017-04 should be applied prospectively and will be effective for the Company's fiscal year beginning October 1, 2020, with early adoption permitted. The Company does not expect this ASU to have a material impact on its consolidated financial statements. ASU 2016-18 – In November 2016, the FASB issued ASU 2016-18, Restricted Cash . This ASU will amend the guidance in ASC Topic 230, Statement of Cash Flows , and is intended to reduce the diversity in the classification and presentation of changes in restricted cash on the statement of cash flows. The amendments within this ASU will require that the reconciliation of the beginning-of-period and end-of-period cash and cash equivalents amounts shown on the statement of cash flows include restricted cash and restricted cash equivalents. If restricted cash and restricted cash equivalents are presented separately from cash and cash equivalents on the balance sheet, an entity will be required to reconcile the amounts presented on the statement of cash flows to the amounts on the balance sheet. An entity will also be required to disclose information regarding the nature of the restrictions. ASU 2016-18 requires retrospective application and became effective for the Company's fiscal year beginning October 1, 2018. The adoption of ASU 2016-18 will change the manner in which restricted cash and restricted cash equivalents are presented in the Company's consolidated financial statements. ASU 2016-16 – In October 2016, the FASB issued ASU 2016-16, Intra-Entity Transfers of Assets Other Than Inventory. This ASU will amend the guidance in ASC Topic 740, Income Taxes . The amendments in this ASU are intended to improve the accounting for the income tax consequences of intra-entity transfers of assets other than inventory by requiring an entity to recognize the income tax consequences when a transfer occurs, instead of when the asset is sold to a third party. ASU 2016-16 requires modified retrospective adoption and became effective for the Company's fiscal year beginning October 1, 2018. The adoption of ASU 2016-16 did not have an impact on the Company's consolidated financial statements. ASU 2016-13 – In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments . The main objective of ASU 2016-13 is to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by an entity at each reporting date. To achieve this objective, the amendments in this update replace the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to develop credit loss estimates. ASU 2016-13 will be effective for the Company's fiscal year beginning October 1, 2020, using a modified retrospective approach. Early adoption is permitted. The Company is currently assessing the impact this ASU will have on its consolidated financial statements. ASU 2016-02 – In February 2016, the FASB issued ASU 2016-02, Leases . This ASU will supersede the guidance in ASC Topic 840, Leases . Under ASU 2016-02, for lease arrangements exceeding a 12-month term, a lessee will be required to recognize in the balance sheet a liability to make lease payments (the lease liability) and a right-of-use asset representing its right to use the underlying asset for the lease term. ASU 2016-02 will retain a distinction between finance and operating leases; however, the principal difference from the previous guidance is that lease assets and liabilities arising from operating leases will be recognized in the balance sheet. The recognition, measurement and presentation of expenses and cash flows arising from a lease by a lessee will not significantly change from current GAAP. The accounting applied by a lessor will be largely unchanged from that applied under current GAAP. Subsequent to issuing ASU 2016-02, the FASB has issued additional standards for the purpose of clarifying certain aspects of ASU 2016-02 and providing an additional (optional) transition method with which to adopt the new leases standard. The subsequently issued ASUs have the same effective date and transition requirements as ASU 2016-02. Under ASU 2016-02, an entity may apply the amendments by using one of the following two methods: (1) recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach or (2) apply the standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. ASU 2016-02 will be effective for the Company's fiscal year beginning October 1, 2019, with early adoption permitted. The Company has not selected a transition method and is currently assessing the impact of this ASU, but does not expect the standard to have a material impact on its net income. Upon adoption of ASU 2016-02, the Company expects to recognize right-of-use assets and lease liabilities for its operating leases, with initial measurement as defined by the ASU, in its Consolidated Balance Sheets. ASU 2014-09 – In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers , to clarify the principles of recognizing revenue from contracts with customers and to improve financial reporting by creating common revenue recognition guidance for U.S. GAAP and International Financial Reporting Standards. This ASU will supersede the revenue recognition requirements in ASC Topic 605, Revenue Recognition, and most industry-specific guidance. Entities are required to apply the following steps when recognizing revenue under ASU 2014-09: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when (or as) the entity satisfies a performance obligation. This ASU also requires additional disclosures related to the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. An entity may apply the amendments by using one of the following two methods: (1) retrospective application to each prior reporting period presented or (2) a modified retrospective approach, requiring the standard be applied only to the most current period presented, with the cumulative effect of initially applying the standard recognized at the date of initial application. ASU 2014-09 is effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period, with early adoption permitted. Subsequent to issuing ASU 2014-09, the FASB has issued additional standards for the purpose of clarifying certain aspects of ASU 2014-09. The subsequently issued ASUs have the same effective date and transition requirements as ASU 2014-09. The guidance does not apply to revenue associated with financial instruments, such as interest revenue, which is accounted for under other GAAP. Accordingly, net interest revenue will not be impacted. The Company adopted the revenue recognition standard as of October 1, 2018 using the modified retrospective method of adoption. This adoption did not have a material impact on the Company's financial condition, results of operations or cash flows as the satisfaction of performance obligations under the new guidance is materially consistent with the Company's previous revenue recognition policies. Similarly, the amended guidance did not have a material impact on the recognition of costs incurred to obtain new contracts with clients. The Company's implementation work is now substantially complete and the additional disclosure requirements will be reflected in interim reporting beginning in the first quarter of fiscal year 2019.
Loss Contingencies (ASC) 450	ASC 450, Loss Contingencies , governs the recognition and disclosure of loss contingencies, including potential losses from legal and regulatory matters. ASC 450 categorizes loss contingencies using three terms based on the likelihood of occurrence of events that result in a loss: "probable" means that "the future event or events are likely to occur;" "remote" means that "the chance of the future event or events occurring is slight;" and "reasonably possible" means that "the chance of the future event or events occurring is more than remote but less than likely." Under ASC 450, the Company accrues for losses that are considered both probable and reasonably estimable.
Fair Value Measurement (ASC) 820-10	ASC 820-10, Fair Value Measurement , defines fair value as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. ASC 820-10 establishes a hierarchy for inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the most observable inputs be used when available. Observable inputs reflect the assumptions market participants would use in pricing the asset or liability, developed based on market data obtained from sources independent of the Company. Unobservable inputs reflect the Company's own assumptions about the assumptions market participants would use in pricing the asset or liability, developed based on the best information available in the circumstances.

Business Acquisition (Tables)

Business Acquisition (Tables)	12 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Schedule of Total Purchase Price	The purchase price for Scottrade was comprised of the following (dollars in millions): TD Ameritrade Holding Corporation common stock issued to the Riney Stockholder and the Escrow Account (1) $ 1,261 Cash paid at closing (2) 3,073 Total purchase price $ 4,334 (1) Represents the value of 27,685,493 shares of the Company's common stock at a price of $45.55 per share. The per share value is based on the opening market price of the Company's common stock as of September 18, 2017, the Acquisition date. As discussed above, the shares held in the Escrow Account were sold and replaced with cash. (2) Includes $1.37 billion of Bank Merger Consideration paid by TD Bank, N.A. to Scottrade, which was used to fund a portion of the Acquisition.
Schedule of Purchase Price Allocation	The purchase price allocation for Scottrade is summarized as follows (dollars in millions): Cash and cash equivalents (1) $ 1,785 Cash and investments segregated and on deposit for regulatory purposes 3,535 Receivable from brokers, dealers and clearing organizations 167 Receivable from clients, net 3,136 Receivable from affiliates 2 Other receivables 54 Securities owned 37 Property and equipment 136 Goodwill 1,760 Acquired intangible assets 974 Deferred tax assets 70 Other assets 35 Total assets acquired 11,691 Payable to brokers, dealers and clearing organizations (354 ) Payable to clients (6,248 ) Accounts payable and other liabilities (272 ) Payable to affiliates (47 ) Long-term debt (2) (436 ) Total liabilities assumed (7,357 ) Total provisional purchase price allocated $ 4,334 (1) Includes $1.37 billion of Bank Merger Consideration paid by TD Bank, N.A. to Scottrade, which was used to fund a portion of the Acquisition. (2) On the date of Acquisition, amounts owed by Scottrade under its 6.125% senior notes, including a prepayment premium, and the amount owed under its 6.18% secured loan were repaid by the Company.
Schedule of Pro Forma Financial Information (Unaudited)	The following table summarizes the unaudited pro forma financial information for the fiscal years indicated (dollars in millions): 2017 2016 (unaudited) Pro forma net revenues $ 4,586 $ 4,158 Pro forma net income $ 921 $ 700 Pro forma basic earnings per share $ 1.62 $ 1.23 Pro forma diluted earnings per share $ 1.62 $ 1.22

Cash and Cash Equivalents (Tabl

Cash and Cash Equivalents (Tables)	12 Months Ended
	Sep. 30, 2018
Cash and Cash Equivalents [Abstract]
Summary of Cash and Cash Equivalents	The Company's cash and cash equivalents is summarized in the following table (dollars in millions): September 30, 2018 2017 Broker-dealer subsidiaries $ 2,094 $ 997 Corporate 342 279 Trust company subsidiary 124 79 Futures commission merchant and forex dealer member subsidiary 89 98 Investment advisory subsidiaries 41 19 Total $ 2,690 $ 1,472

Cash and Investments Segregat_2

Cash and Investments Segregated and on Deposit for Regulatory Purposes (Tables)	12 Months Ended
	Sep. 30, 2018
Restricted Cash and Investments [Abstract]
Cash and Investments Segregated and on Deposit for Regulatory Purposes	Cash and investments segregated and on deposit for regulatory purposes consists of the following (dollars in millions): September 30, 2018 2017 U.S. government agency mortgage-backed securities $ 1,302 $ 1,486 Cash in demand deposit accounts 956 3,653 Reverse repurchase agreements (collateralized by U.S. government debt securities) 500 1,004 Cash on deposit with futures commission merchants 202 209 U.S. government debt securities 200 4,019 U.S. government debt securities on deposit with futures commission merchant 25 75 Total $ 3,185 $ 10,446

Receivable from and Payable t_2

Receivable from and Payable to Brokers, Dealers and Clearing Organizations (Tables)	12 Months Ended
	Sep. 30, 2018
Brokers and Dealers [Abstract]
Amounts Receivable from and Payable to Brokers, Dealers and Clearing Organizations	Amounts receivable from and payable to brokers, dealers and clearing organizations consist of the following (dollars in millions): September 30, 2018 2017 Receivable: Deposits paid for securities borrowed $ 803 $ 1,154 Clearing organizations 545 151 Broker-dealers 14 21 Securities failed to deliver 12 8 Total $ 1,374 $ 1,334 Payable: Deposits received for securities loaned $ 2,914 $ 2,449 Securities failed to receive 34 21 Clearing organizations 29 32 Broker-dealers 3 2 Total $ 2,980 $ 2,504

Allowance for Doubtful Accoun_2

Allowance for Doubtful Accounts on Receivables (Tables)	12 Months Ended
	Sep. 30, 2018
Receivables [Abstract]
Allowance for Credit Losses on Financing Receivables	The following table summarizes activity in the Company's allowance for doubtful accounts on client and other receivables for the fiscal years indicated (dollars in millions): 2018 2017 2016 Beginning balance $ 11 $ 9 $ 12 Provision for doubtful accounts, net 56 2 2 Acquired in business acquisition — 2 — Write-off of doubtful accounts (13 ) (2 ) (5 ) Ending balance $ 54 $ 11 $ 9

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consists of the following (dollars in millions): September 30, 2018 2017 Buildings and building components $ 462 $ 351 Computer equipment 326 270 Software 178 215 Leasehold improvements 176 173 Building construction in process — 101 Land 61 77 Other property and equipment 92 83 1,295 1,270 Less: Accumulated depreciation and amortization (503 ) (518 ) Property and equipment at cost, net $ 792 $ 752

Goodwill and Acquired Intangi_2

Goodwill and Acquired Intangible Assets (Tables)	12 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes in the Carrying Amount of Goodwill	The following table summarizes changes in the carrying amount of goodwill (dollars in millions): Balance as of September 30, 2016 $ 2,467 Goodwill recorded in acquisition of Scottrade (see Note 2) 1,746 Balance as of September 30, 2017 4,213 Purchase accounting adjustments (1) 14 Balance as of September 30, 2018 $ 4,227 (1) The purchasing accounting adjustments are primarily attributable to post-closing adjustments related to the Bank Merger Consideration, property acquired and liabilities assumed in the acquisition of Scottrade. The purchase price allocation was finalized during September 2018, one-year from the anniversary of the Acquisition. Differences between purchase accounting estimates and actual results that arose prior to September 18, 2018 resulted in adjustments to the purchase price allocation. Any such adjustments arising on or after September 18, 2018 will be recorded in earnings.
Acquired Intangible Assets	Acquired intangible assets consist of the following (dollars in millions): September 30, 2018 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Client relationships $ 2,183 $ (1,003 ) $ 1,180 $ 2,183 $ (877 ) $ 1,306 Technology and content 108 (108 ) — 108 (100 ) 8 Trade names 10 (7 ) 3 10 — 10 Trademark license 146 — 146 146 — 146 $ 2,447 $ (1,118 ) $ 1,329 $ 2,447 $ (977 ) $ 1,470
Estimated Future Amortization Expense for Acquired Intangible Assets	Estimated future amortization expense for acquired finite-lived intangible assets outstanding as of September 30, 2018 is as follows (dollars in millions): Fiscal Year Estimated Amortization Expense 2019 $ 124 2020 116 2021 106 2022 105 2023 75 Thereafter (to 2035) 657 Total $ 1,183

Exit Liabilities (Tables)

Exit Liabilities (Tables)	12 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Summary of the Activity in Exit Liabilities	The following table summarizes activity in the Company's exit liabilities for the fiscal years ended September 30, 2018 and 2017, which are included in accounts payable and other liabilities on the Consolidated Balance Sheets (dollars in millions): Severance Pay and Other Employment Benefits Contract Termination and Other Costs Total Balance, September 30, 2016 $ 4 $ — $ 4 Exit liabilities assumed in business acquisition 100 — 100 Costs incurred and charged to expense 43 (1) 1 (2) 44 Costs paid or otherwise settled (9 ) (1 ) (10 ) Balance, September 30, 2017 138 — 138 Exit liabilities assumed - post closing adjustments — 9 9 Costs incurred and charged to expense 235 (1) 213 (2) 448 Costs paid or otherwise settled (352 ) (174 ) (526 ) Balance, September 30, 2018 $ 21 $ 48 $ 69 (1) Costs incurred for severance pay and other employment benefits are included in employee compensation and benefits on the Consolidated Statements of Income. (2) Costs incurred for contract termination and other costs are primarily included in other operating expense and professional services on the Consolidated Statements of Income.
Summary of the Cumulative Amount of Acquisition-Related Exit Costs	The following table summarizes the cumulative amount of acquisition related exit costs incurred by the Company related to the Scottrade acquisition as of September 30, 2018 (dollars in millions): Severance Pay and Other Employment Benefits Contract Termination and Other Costs Total Exit liabilities assumed in business acquisition $ 100 $ 9 $ 109 Employee compensation and benefits 267 — 267 Clearing and execution costs — 1 1 Communications — 1 1 Occupancy and equipment costs — 7 7 Professional services — 30 30 Other operating expense — 173 173 Other non-operating expense — 2 2 Total $ 367 $ 223 $ 590

Long-term Debt and Other Borr_2

Long-term Debt and Other Borrowings (Tables)	12 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of Long-term Debt and Other Borrowings	Long-term debt and other borrowings consist of the following (dollars in millions): September 30, 2018 Face Value Unamortized Discounts and Debt Issuance Costs Fair Value Adjustment (1) Net Carrying Value Other borrowings: Securities sold under agreements to repurchase $ 96 $ — $ — $ 96 Long-term debt: Senior Notes: 5.600% Notes due 2019 500 (1 ) 2 501 2.950% Notes due 2022 750 (4 ) (27 ) 719 3.625% Notes due 2025 500 (3 ) (17 ) 480 3.300% Notes due 2027 800 (9 ) (52 ) 739 Subtotal - Long-term debt 2,550 (17 ) (94 ) 2,439 Total long-term debt and other borrowings $ 2,646 $ (17 ) $ (94 ) $ 2,535 September 30, 2017 Face Value Unamortized Discounts and Debt Issuance Costs Fair Value Adjustment (1) Net Carrying Value Other borrowings: Securities sold under agreements to repurchase $ 97 $ — $ — $ 97 Long-term debt: Senior Notes: 5.600% Notes due 2019 500 (1 ) 15 514 2.950% Notes due 2022 750 (5 ) — 745 3.625% Notes due 2025 500 (3 ) 11 508 3.300% Notes due 2027 800 (9 ) (3 ) 788 Subtotal - Long-term debt 2,550 (18 ) 23 2,555 Total long-term debt and other borrowings $ 2,647 $ (18 ) $ 23 $ 2,652 (1) Fair value adjustments relate to changes in the fair value of the debt while in a fair value hedging relationship. See " Fair Value Hedging " below.
Fiscal Year Maturities on Long-term Debt Outstanding	Fiscal year maturities on long-term debt outstanding at September 30, 2018 are as follows (dollars in millions): 2019 $ — 2020 500 2021 — 2022 750 2023 — Thereafter 1,300 Total $ 2,550
Summary of Key Information About Senior Notes	Key information about the committed and/or uncommitted lines of credit is summarized in the following table (dollars in millions): Borrower Subsidiary Committed Facility Uncommitted Facility (1) Termination Date TD Ameritrade Clearing, Inc. $400 $300 March 1, 2022 TD Ameritrade, Inc. N/A $300 March 1, 2022 TD Ameritrade Futures & Forex LLC $45 N/A August 11, 2021 (1) The Parent is permitted, but under no obligation, to make loans under uncommitted facilities. Key information about the Senior Notes outstanding as of September 30, 2018 is summarized in the following table (dollars in millions): Description Date Issued Maturity Date Aggregate Principal Interest Rate 2019 Notes November 25, 2009 December 1, 2019 $500 5.600% 2022 Notes March 4, 2015 April 1, 2022 $750 2.950% 2025 Notes October 17, 2014 April 1, 2025 $500 3.625% 2027 Notes April 27, 2017 April 1, 2027 $800 3.300% Key information regarding the recent debt issuance is summarized in the following table (dollars in millions): Description Date Issued Maturity Date Aggregate Principal Interest Rate 2021 Notes October 30, 2018 November 1, 2021 $600 Variable 2024 Notes October 30, 2018 April 1, 2024 $400 3.75%
Gains and Losses Resulting from Changes in Fair Value of Interest Rate Swaps and Hedged Fixed Rate Debt	The following table summarizes gains and losses resulting from changes in the fair value of interest rate swaps designated as fair value hedges and the hedged fixed-rate debt for the fiscal years indicated (dollars in millions): 2018 2017 2016 Gain (loss) on fair value of interest rate swaps $ (117 ) $ (56 ) $ 16 Gain (loss) on fair value of hedged fixed-rate debt 117 56 (16 ) Net gain (loss) recorded in interest on borrowings $ — $ — $ —
Schedule of the Fair Value of Outstanding Derivatives Designated as Hedging Instruments on the Consolidated Balance Sheets	The following table summarizes the classification and the fair value of outstanding derivatives designated as hedging instruments on the Consolidated Balance Sheets (dollars in millions): September 30, 2018 2017 Pay-variable interest rate swaps designated as fair value hedges: Other assets $ 2 $ 26 Accounts payable and other liabilities $ (96 ) $ (3 )

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Provision for Income Taxes	Provision for income taxes is comprised of the following for the fiscal years indicated (dollars in millions): 2018 2017 2016 Current expense (benefit): Federal $ 380 $ 484 $ 435 State 58 49 (4 ) 438 533 431 Deferred expense (benefit): Federal (32 ) (11 ) (5 ) State 8 — (3 ) (24 ) (11 ) (8 ) Provision for income taxes $ 414 $ 522 $ 423
Reconciliation of Federal Statutory Tax Rate to Effective Tax Rate	A reconciliation of the U.S. federal statutory income tax rate to the effective tax rate applicable to pre-tax income follows for the fiscal years indicated: 2018 2017 2016 Federal statutory income tax rate 24.5 % 35.0 % 35.0 % Statutory versus actual blended federal income tax rate (1.3 ) — — State taxes, net of federal tax effect 2.6 2.8 2.8 Adjustments to estimated state income taxes — — (0.2 ) Federal incentives 0.4 (0.3 ) (1.4 ) Interest recorded (reversed) on unrecognized tax benefits, net 0.2 0.2 (1.1 ) Remeasurement of U.S. deferred income taxes (3.8 ) — — Reversal of accruals for unrecognized tax benefits (0.4 ) (0.4 ) (1.8 ) Share-based payment compensation (0.3 ) — — Other — 0.1 0.1 21.9 % 37.4 % 33.4 %
Deferred Tax Assets (Liabilities)	Deferred tax assets (liabilities) are comprised of the following (dollars in millions): September 30, 2018 2017 Deferred tax assets: Accrued and other liabilities $ 78 $ 131 Stock-based compensation 19 28 Allowance for doubtful accounts 14 6 Unrecognized loss on cash flow hedging instruments 9 15 Intangible assets, state tax benefit 3 5 Operating loss carryforwards 2 1 Gross deferred tax assets 125 186 Less: Valuation allowance (2 ) (1 ) Net deferred tax assets 123 185 Deferred tax liabilities: Acquired intangible assets (236 ) (331 ) Property and equipment (46 ) (35 ) Prepaid expenses (13 ) (11 ) Unrealized gain on investments (2 ) — Other deferred tax liabilities (3 ) (1 ) Total deferred tax liabilities (300 ) (378 ) Net deferred tax liabilities $ (177 ) $ (193 )
Reconciliation of Activity Related to Unrecognized Tax Benefits	A reconciliation of the activity related to unrecognized tax benefits follows for the fiscal years indicated (dollars in millions): 2018 2017 2016 Beginning balance $ 152 $ 142 $ 154 Additions based on tax positions related to the current year 35 28 30 Additions for tax positions of prior years 8 — 20 Reductions due to lapsed statute of limitations (9 ) (7 ) (8 ) Reductions due to settlements with taxing authorities (3 ) (1 ) (21 ) Reductions for tax positions of prior years (2 ) (10 ) (33 ) Ending balance $ 181 $ 152 $ 142

Capital Requirements (Tables)

Capital Requirements (Tables)	12 Months Ended
	Sep. 30, 2018
Regulatory Capital Requirements [Abstract]
Net Capital and Net Capital Requirements for Company's Broker-dealer Subsidiaries	Net capital and net capital requirements for the Company's broker-dealer subsidiaries are summarized in the following tables (dollars in millions): TD Ameritrade Clearing, Inc. Date Net Capital Required Net Capital (2% of Aggregate Debit Balances) Net Capital in Excess of Required Net Capital Ratio of Net Capital to Aggregate Debit Balances September 30, 2018 $ 2,831 $ 525 $ 2,306 10.79 % September 30, 2017 $ 1,595 $ 340 $ 1,255 9.39 % TD Ameritrade, Inc. Date Net Capital Required Net Capital (Minimum Dollar Requirement) Net Capital in Excess of Required Net Capital September 30, 2018 $ 181 $ 0.25 $ 181 September 30, 2017 $ 155 $ 0.25 $ 155 Scottrade, Inc. Date Net Capital Required Net Capital (2% of Aggregate Debit Balances) Net Capital in Excess of Required Net Capital Ratio of Net Capital to Aggregate Debit Balances September 30, 2018 (1) N/A N/A N/A N/A September 30, 2017 $ 348 $ 70 $ 278 9.99 % (1) On February 26, 2018, Scottrade, Inc. transferred substantially all of its broker-dealer business net assets, including its clearing operations, to other subsidiaries of the Company. The Company's request to withdraw Scottrade, Inc.'s registration as a broker-dealer was granted and the withdrawal became effective on September 7, 2018.
Adjusted Net Capital and Adjusted Net Capital Requirements for Company's FCM and FDM Subsidiary	Adjusted net capital and adjusted net capital requirements for the Company's FCM and FDM subsidiary are summarized in the following table (dollars in millions): TD Ameritrade Futures & Forex LLC Date Adjusted Net Capital Required Adjusted Net Capital ($20 Million Plus 5% of All Foreign Exchange Liabilities Owed to Forex Clients in Excess of $10 Million) Adjusted Net Capital in Excess of Required Adjusted Net Capital September 30, 2018 $ 129 $ 23 $ 106 September 30, 2017 $ 77 $ 22 $ 55

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Option Activity in Stock Incentive Plans	The following is a summary of option activity in the Company's stock incentive plans for the fiscal year ended September 30, 2018 : Number of Options (in thousands) Weighted Average Exercise Price Weighted Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (in millions) Outstanding at beginning and end of year 503 $ 27.97 7.3 $ 13 Exercisable at end of year 252 $ 27.97 7.3 $ 6
Summary of Assumptions used for Estimation of Fair Value of Stock Options Granted	The fair value of stock options granted during fiscal year 2016 was estimated using a Black-Scholes-Merton valuation model with the following inputs: Risk-free interest rate 1.73 % Expected dividend yield 2.4 % Expected volatility 27 % Expected option life (years) 6.5
Summary of Restricted Stock Unit Activity in Stock Incentive Plans	The following is a summary of RSU activity in the Company's stock incentive plans for the fiscal year ended September 30, 2018 : Number of Units (in thousands) Weighted Average Grant Date Fair Value Nonvested at beginning of year 2,394 $ 34.83 Granted 671 $ 50.61 Vested (807 ) $ 33.24 Forfeited (129 ) $ 41.72 Nonvested at end of year 2,129 $ 39.99
Summary of Performance Restricted Stock Unit Activity in Stock Incentive Plans	The following is a summary of PRSU activity in the Company's stock incentive plans for the fiscal year ended September 30, 2018 : Number of Units (in thousands) Weighted Average Grant Date Fair Value Nonvested at beginning of year 265 $ 39.48 Granted 235 $ 49.50 Nonvested at end of year 500 $ 44.19
Summary of Assumptions used for Estimation of Fair Value of PRSUs Granted	The fair value of PRSUs granted was estimated using a Monte Carlo simulation model with the following inputs for the fiscal years indicated: 2018 2017 Risk-free interest rate 1.84 % 1.34 % Expected dividend yield 0 % 0 % Expected volatility 28 % 27 % Expected term (years) 2.8 2.9

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Summary of Future Minimum Rental Commitments Under Non-Cancelable Operating Leases	The Company has various non-cancelable operating leases on facilities requiring annual payments as follows (dollars in millions): Fiscal Year Minimum Lease Payments Sublease Income Net Lease Commitments 2019 $ 75 $ (1 ) $ 74 2020 64 (1 ) 63 2021 45 — 45 2022 34 — 34 2023 28 — 28 Thereafter (to 2033) 99 — 99 Total $ 345 $ (2 ) $ 343
Summary of Collateral Available, Loaned or Repledged	The following table summarizes the fair values of client margin securities and stock borrowings that were available to the Company to utilize as collateral on various borrowings or for other purposes, and the amount of that collateral loaned or repledged by the Company (dollars in billions): September 30, 2018 2017 Client margin securities $ 31.4 $ 23.8 Stock borrowings 0.8 1.2 Total collateral available $ 32.2 $ 25.0 Collateral loaned $ 2.9 $ 2.4 Collateral repledged 6.3 4.1 Total collateral loaned or repledged $ 9.2 $ 6.5
Summary of Cash Deposited with and Securities Pledged to Clearinghouses	The following table summarizes cash deposited with and securities pledged to clearinghouses by the Company (dollars in millions): September 30, Assets Balance Sheet Classification 2018 2017 Cash Receivable from brokers, dealers and clearing organizations $ 545 $ 151 U.S. government debt securities Securities owned, at fair value 50 398 Total $ 595 $ 549

Fair Value Disclosures (Tables)

Fair Value Disclosures (Tables)	12 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value Hierarchy for Assets and Liabilities Measured on Recurring Basis	The following tables present the Company's fair value hierarchy for assets and liabilities measured at fair value on a recurring basis as of September 30, 2018 and 2017 (dollars in millions): As of September 30, 2018 Level 1 Level 2 Level 3 Fair Value Assets: Cash equivalents: Money market mutual funds $ 2,373 $ — $ — $ 2,373 Investments segregated and on deposit for regulatory purposes: U.S. government debt securities — 225 — 225 U.S. government agency mortgage-backed securities — 1,302 — 1,302 Subtotal - Investments segregated for regulatory purposes — 1,527 — 1,527 Securities owned: U.S. government debt securities — 149 — 149 Other 1 6 — 7 Subtotal - Securities owned 1 155 — 156 Investments available-for-sale: U.S. government debt securities — 484 — 484 Other assets: Pay-variable interest rate swaps (1) — 2 — 2 U.S. government debt securities — 1 — 1 Auction rate securities — — 1 1 Subtotal - Other assets — 3 1 4 Total assets at fair value $ 2,374 $ 2,169 $ 1 $ 4,544 Liabilities: Accounts payable and other liabilities: Pay-variable interest rate swaps (1) $ — $ 96 $ — $ 96 (1) See " Fair Value Hedging " in Note 10 for details. As of September 30, 2017 Level 1 Level 2 Level 3 Fair Value Assets: Cash equivalents: Money market mutual funds $ 1,081 $ — $ — $ 1,081 Investments segregated and on deposit for regulatory purposes: U.S. government debt securities — 4,094 — 4,094 U.S. government agency mortgage-backed securities — 1,486 — 1,486 Subtotal - Investments segregated for regulatory purposes — 5,580 — 5,580 Securities owned: U.S. government debt securities — 498 — 498 Other 1 4 — 5 Subtotal - Securities owned 1 502 — 503 Investments available-for-sale: U.S. government debt securities — 746 — 746 Other assets: Pay-variable interest rate swaps (1) — 26 — 26 U.S. government debt securities — 1 — 1 Auction rate securities — — 1 1 Subtotal - Other assets — 27 1 28 Total assets at fair value $ 1,082 $ 6,855 $ 1 $ 7,938 Liabilities: Accounts payable and other liabilities: Pay-variable interest rate swaps (1) $ — $ 3 $ — $ 3 (1) See " Fair Value Hedging " in Note 10 for details.

Offsetting Assets and Liabili_2

Offsetting Assets and Liabilities (Tables)	12 Months Ended
	Sep. 30, 2018
Offsetting [Abstract]
Effect of Rights of Setoff Associated with Company's Recognized Assets and Liabilities	The following tables present information about the potential effect of rights of setoff associated with the Company's recognized assets and liabilities as of September 30, 2018 and 2017 (dollars in millions): September 30, 2018 Gross Amounts Not Offset in the Consolidated Balance Sheet Gross Amounts of Recognized Assets and Liabilities Gross Amounts Offset in the Consolidated Balance Sheet Net Amounts Presented in the Consolidated Balance Sheet Financial Instruments (5) Collateral Received or Pledged (Including Cash) (6) Net Amount (7) Assets: Investments segregated for regulatory purposes: Reverse repurchase agreements $ 500 $ — $ 500 $ — $ (500 ) $ — Receivable from brokers, dealers and clearing organizations: Deposits paid for securities borrowed (1) 803 — 803 (41 ) (744 ) 18 Other assets: Pay-variable interest rate swaps 2 — 2 (2 ) — — Total $ 1,305 $ — $ 1,305 $ (43 ) $ (1,244 ) $ 18 Liabilities: Payable to brokers, dealers and clearing organizations: Deposits received for securities loaned (2)(3) $ 2,914 $ — $ 2,914 $ (43 ) $ (2,544 ) $ 327 Securities sold under agreements to repurchase (4) 96 — 96 (96 ) — — Accounts payable and other liabilities: Pay-variable interest rate swaps 96 — 96 (82 ) — 14 Total $ 3,106 $ — $ 3,106 $ (221 ) $ (2,544 ) $ 341 September 30, 2017 Gross Amounts Not Offset in the Consolidated Balance Sheet Gross Amounts of Recognized Assets and Liabilities Gross Amounts Offset in the Consolidated Balance Sheet Net Amounts Presented in the Consolidated Balance Sheet Financial Instruments (5) Collateral Received or Pledged (Including Cash) (6) Net Amount (7) Assets: Investments segregated for regulatory purposes: Reverse repurchase agreements $ 1,004 $ — $ 1,004 $ — $ (1,004 ) $ — Receivable from brokers, dealers and clearing organizations: Deposits paid for securities borrowed (1) 1,154 — 1,154 (110 ) (1,023 ) 21 Other assets: Pay-variable interest rate swaps 26 — 26 (26 ) — — Reverse repurchase agreements 65 — 65 — (65 ) — Total other assets 91 — 91 (26 ) (65 ) — Total $ 2,249 $ — $ 2,249 $ (136 ) $ (2,092 ) $ 21 Liabilities: Payable to brokers, dealers and clearing organizations: Deposits received for securities loaned (2)(3) $ 2,449 $ — $ 2,449 $ (112 ) $ (2,113 ) $ 224 Securities sold under agreements to repurchase (4) 97 — 97 (97 ) — — Accounts payable and other liabilities: Pay-variable interest rate swaps 3 — 3 (1 ) — 2 Total $ 2,549 $ — $ 2,549 $ (210 ) $ (2,113 ) $ 226 (1) Included in the gross amounts of deposits paid for securities borrowed is $462 million and $675 million as of September 30, 2018 and 2017 , respectively, transacted through a risk-sharing program with the OCC, which guarantees the return of cash to the Company. See " General Contingencies " in Note 15 for a discussion of the potential risks associated with securities borrowing transactions and how the Company mitigates those risks. (2) Included in the gross amounts of deposits received for securities loaned is $2.01 billion and $1.65 billion as of September 30, 2018 and 2017 , respectively, transacted through a risk-sharing program with the OCC, which guarantees the return of securities to the Company. See " General Contingencies " in Note 15 for a discussion of the potential risks associated with securities lending transactions and how the Company mitigates those risks. (3) Substantially all of the Company's securities lending transactions have a continuous contractual term and, upon notice by either party, may be terminated within two business days. The following table summarizes the Company's gross liability for securities lending transactions by the class of securities loaned (dollars in millions): September 30, 2018 2017 Deposits received for securities loaned: Equity securities $ 2,583 $ 2,109 Exchange-traded funds 223 230 Closed-end funds 74 66 Other 34 44 Total $ 2,914 $ 2,449 (4) The collateral pledged includes available-for-sale U.S. government debt securities at fair value. All of the Company's repurchase agreements have a remaining contractual maturity of less than 90 days and, upon default by either party, may be terminated at the option of the non-defaulting party. See " General Contingencies " in Note 15 for a discussion of the potential risks associated with repurchase agreements and how the Company mitigates those risks. (5) Amounts represent recognized assets and liabilities that are subject to enforceable master agreements with rights of setoff. (6) Represents the fair value of collateral the Company had received or pledged under enforceable master agreements, limited for table presentation purposes to the net amount of the recognized assets due from or liabilities due to each counterparty. At September 30, 2018 and 2017 , the Company had received total collateral with a fair value of $1.30 billion and $2.26 billion , respectively, and pledged total collateral with a fair value of $2.76 billion and $2.32 billion , respectively. (7) Represents the amount for which, in the case of net recognized assets, the Company had not received collateral, and in the case of net recognized liabilities, the Company had not pledged collateral.
Disaggregation of Gross Secured Lending Transactions	The following table summarizes the Company's gross liability for securities lending transactions by the class of securities loaned (dollars in millions): September 30, 2018 2017 Deposits received for securities loaned: Equity securities $ 2,583 $ 2,109 Exchange-traded funds 223 230 Closed-end funds 74 66 Other 34 44 Total $ 2,914 $ 2,449

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	12 Months Ended
	Sep. 30, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Comprehensive Income (Loss)	The following table presents the net change in fair value recorded for each component of other comprehensive income (loss) before and after income tax for the fiscal years indicated (dollars in millions): 2018 2017 2016 Before Tax Tax Effect Net of Tax Before Tax Tax Effect Net of Tax Before Tax Tax Effect Net of Tax Investments available-for-sale: Unrealized loss $ (12 ) $ 3 $ (9 ) $ (9 ) $ 4 $ (5 ) $ — $ — $ — Reclassification adjustment for realized loss included in net income (1) 11 (4 ) 7 — — — — — — Net change in investments available-for-sale (1 ) (1 ) (2 ) (9 ) 4 (5 ) — — — Cash flow hedging instruments: Reclassification adjustment for portion of realized loss amortized to net income (2) 5 (1 ) 4 4 (2 ) 2 5 (2 ) 3 Net change in cash flow hedging instruments 5 (1 ) 4 4 (2 ) 2 5 (2 ) 3 Other comprehensive income (loss) $ 4 $ (2 ) $ 2 $ (5 ) $ 2 $ (3 ) $ 5 $ (2 ) $ 3 (1) The before tax reclassification amount and related tax effect are included in loss on sale of investments and provision for income taxes, respectively, on the Consolidated Statements of Income. (2) The before tax reclassification amounts and the related tax effects are included in interest on borrowings and provision for income taxes, respectively, on the Consolidated Statements of Income.
Schedule of Accumulated Other Comprehensive Income (Loss)	The following table presents after-tax changes in each component of accumulated other comprehensive loss for the fiscal years indicated (dollars in millions): 2018 2017 2016 Investments available-for-sale: Beginning balance $ (5 ) $ — $ — Other comprehensive loss before reclassification (9 ) (5 ) — Amount reclassified from accumulated other comprehensive loss 7 — — Current period change (2 ) (5 ) — Ending balance $ (7 ) $ (5 ) $ — Cash flow hedging instruments: Beginning balance $ (20 ) $ (22 ) $ (25 ) Amount reclassified from accumulated other comprehensive loss 4 2 3 Adoption of Accounting Standards Update 2018-02 (Note 1) (4 ) — — Current period change — 2 3 Ending balance $ (20 ) $ (20 ) $ (22 ) Total accumulated other comprehensive loss: Beginning balance $ (25 ) $ (22 ) $ (25 ) Current period change (2 ) (3 ) 3 Ending balance $ (27 ) $ (25 ) $ (22 )

Related Party Transactions (Tab

Related Party Transactions (Tables)	12 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	The following tables summarize revenues and expenses resulting from transactions with TD and its affiliates for the fiscal years indicated (dollars in millions): Description Statement of Income Classification Revenues from TD and its Affiliates 2018 2017 2016 Insured Deposit Account Agreement Bank deposit account fees $ 1,426 $ 1,101 $ 926 Mutual Fund Agreements Investment product fees 17 15 11 Other Various 13 10 7 Total revenues $ 1,456 $ 1,126 $ 944 Description Statement of Income Classification Expenses to TD and its Affiliates 2018 2017 2016 Canadian Call Center Services Agreement (1) Various $ — $ 11 $ 22 Referral and Strategic Alliance Agreement Other expense 5 5 3 Other Various 2 1 1 Total expenses $ 7 $ 17 $ 26 (1) The Company notified TD of its intent to not extend or renew the Canadian Call Center Services Agreement and services under this agreement ended by September 30, 2017 . The following table summarizes the classification and amount of receivables from and payables to TD and its affiliates on the Consolidated Balance Sheets resulting from related party transactions (dollars in millions): September 30, 2018 2017 Assets: Receivable from affiliates $ 151 $ 110 Liabilities: Payable to brokers, dealers and clearing organizations $ 47 $ 37 Payable to affiliates 7 38

Condensed Financial Informati_2

Condensed Financial Information (Parent Company Only) (Tables)	12 Months Ended
	Sep. 30, 2018
Condensed Financial Information Disclosure [Abstract]
Schedule of Condensed Balance Sheets (Parent Company Only)	PARENT COMPANY ONLY CONDENSED BALANCE SHEETS As of September 30, 2018 and 2017 2018 2017 (In millions) ASSETS Cash and cash equivalents $ 151 $ 154 Receivable from subsidiaries 8 6 Investments available-for-sale, at fair value (including $98 million and $99 million of securities pledged as collateral for repurchase agreements at September 30, 2018 and 2017, respectively) 484 746 Investments in subsidiaries 9,976 9,043 Other, net 162 108 Total assets $ 10,781 $ 10,057 LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities: Accounts payable and other liabilities $ 240 $ 104 Payable to subsidiaries and affiliates 3 54 Securities sold under agreements to repurchase 96 97 Long-term debt 2,439 2,555 Total liabilities 2,778 2,810 Stockholders' equity 8,003 7,247 Total liabilities and stockholders' equity $ 10,781 $ 10,057
Schedule of Condensed Statements of Income (Parent Company Only)	PARENT COMPANY ONLY CONDENSED STATEMENTS OF INCOME For the Years Ended September 30, 2018 , 2017 and 2016 2018 2017 2016 (In millions) Net revenues $ 52 $ 31 $ 30 Operating expenses 21 34 26 Operating income (loss) 31 (3 ) 4 Other expense 106 71 53 Loss before income taxes and equity in income of subsidiaries (75 ) (74 ) (49 ) Provision for (benefit from) income taxes 15 (22 ) 6 Loss before equity in income of subsidiaries (90 ) (52 ) (55 ) Equity in income of subsidiaries 1,563 924 897 Net income $ 1,473 $ 872 $ 842
Schedule of Condensed Statements of Cash Flows (Parent Company Only)	PARENT COMPANY ONLY CONDENSED STATEMENTS OF CASH FLOWS For the Years Ended September 30, 2018 , 2017 and 2016 2018 2017 2016 (In millions) Cash flows from operating activities: Net income $ 1,473 $ 872 $ 842 Adjustments to reconcile net income to net cash flows provided by operating activities: Equity in income of subsidiaries (1,563 ) (924 ) (897 ) Deferred income taxes 13 (12 ) — Dividends from subsidiaries 1,030 1,230 825 Loss on sale of investments 11 — — Stock-based compensation 60 36 34 Other, net 9 9 8 Changes in operating assets and liabilities: Receivable from subsidiaries (2 ) 2 (3 ) Other assets (92 ) — 1 Accounts payable and other liabilities 42 (67 ) 38 Payable to subsidiaries and affiliates (24 ) (4 ) 26 Net cash provided by operating activities 957 1,142 874 Cash flows from investing activities: Investment in subsidiaries (425 ) (15 ) (60 ) Loans made under intercompany credit agreements (175 ) — — Collections on intercompany credit agreements 175 — — Cash paid in business acquisition (4 ) (1,698 ) — Proceeds from sale of investments available-for-sale, at fair value 643 — — Purchase of investments available-for-sale, at fair value (392 ) — (757 ) Proceeds from sale and maturity of short-term investments — — 600 Purchase of short-term investments — — (601 ) Net cash used in investing activities (178 ) (1,713 ) (818 ) Cash flows from financing activities: Proceeds from issuance of long-term debt — 798 — Payment of debt issuance costs (3 ) (8 ) — Principal payments on long-term debt — (385 ) — Reimbursement (payment) of prepayment premium on long-term debt 2 (54 ) — Net proceeds from (payments on) securities sold under agreements to repurchase (1 ) 97 — Proceeds from Parent Senior Revolving Facility 200 — — Principal payments on Parent Senior Revolving Facility (200 ) — — Payment of cash dividends (477 ) (379 ) (362 ) Proceeds from issuance of common stock — 400 — Purchase of treasury stock (255 ) — (352 ) Purchase of treasury stock for income tax withholding on stock-based compensation (17 ) (27 ) (30 ) Payment for future treasury stock under accelerated stock repurchase agreement (31 ) — — Other, net — 35 16 Net cash provided by (used in) financing activities (782 ) 477 (728 ) Net decrease in cash and cash equivalents (3 ) (94 ) (672 ) Cash and cash equivalents at beginning of year 154 248 920 Cash and cash equivalents at end of year $ 151 $ 154 $ 248 Supplemental cash flow information: Interest paid $ 94 $ 50 $ 47 Income taxes paid $ 309 $ 452 $ 488 Noncash investing activities: Issuance of common stock in acquisition $ — $ 1,261 $ — Assets transferred to a subsidiary, net $ — $ 15 $ —

Quarterly Data (Unaudited) (Tab

Quarterly Data (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Data	(Dollars in millions, except per share amounts) For the Fiscal Year Ended September 30, 2018 First Quarter Second Quarter Third Fourth Net revenues $ 1,257 $ 1,415 $ 1,382 $ 1,398 Operating income $ 336 $ 396 $ 631 $ 635 Net income $ 297 $ 271 $ 451 $ 454 Basic earnings per share $ 0.52 $ 0.48 $ 0.79 $ 0.80 Diluted earnings per share $ 0.52 $ 0.48 $ 0.79 $ 0.80 For the Fiscal Year Ended September 30, 2017 First Quarter Second Quarter Third Quarter Fourth Net revenues $ 859 $ 904 $ 931 $ 983 Operating income $ 353 $ 358 $ 394 $ 361 Net income $ 216 $ 214 $ 231 $ 211 Basic earnings per share $ 0.41 $ 0.41 $ 0.44 $ 0.40 Diluted earnings per share $ 0.41 $ 0.40 $ 0.44 $ 0.39 Quarterly amounts may not sum to fiscal year totals due to rounding.

Nature of Operations and Summ_3

Nature of Operations and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) shares in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash and Cash Equivalents
Maturity period of cash equivalents (three months or less)		3 months
Cash and Investments Segregated and on Deposit for Regulatory Purposes
General maturity of reverse repurchase agreements, collateralized by U.S. Treasury securities		7 days
Investments Available-for-sale
Available-for-sale securities, unrealized gain (loss)		$ 0	$ 0
Goodwill and Amortization of Acquired Intangible Assets
Amount of impairment charges resulting from the annual goodwill impairment tests		0	0	$ 0
Long-Lived Assets and Acquired Intangible Assets
Property and equipment, net	$ 792,000,000	792,000,000	752,000,000
Amount of impairment charges resulting from the annual intangible assets impairment tests		$ 0	$ 0	$ 0
Transaction-based Revenues
Client securities transactions, trade settlement, number of business days		2 days
Earnings Per Share
Antidilutive awards excluded from calculation of diluted earnings per share (in shares)		0	0	0.4
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Provision for (benefit from) income taxes		$ 414,000,000	$ 522,000,000	$ 423,000,000
Minimum [Member]
Goodwill and Amortization of Acquired Intangible Assets
Estimated useful life, intangible assets		2 years
Income Taxes
Percent likelihood for tax benefit amounts to be realized upon settlement		50.00%
Maximum [Member]
Investments Available-for-sale
Available-for-sale debt maturities, in years		6 years
Goodwill and Amortization of Acquired Intangible Assets
Estimated useful life, intangible assets		23 years
Long Lived Assets Held-for-sale [Member]
Long-Lived Assets and Acquired Intangible Assets
Property and equipment, net	36,000,000	$ 36,000,000	$ 5,000,000
Building and Building Components [Member] | Minimum [Member]
Property and Equipment
Estimated useful life, property and equipment		7 years
Building and Building Components [Member] | Maximum [Member]
Property and Equipment
Estimated useful life, property and equipment		40 years
Other Depreciable Property and Equipment [Member] | Minimum [Member]
Property and Equipment
Estimated useful life, property and equipment		3 years
Other Depreciable Property and Equipment [Member] | Maximum [Member]
Property and Equipment
Estimated useful life, property and equipment		7 years
Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Adoption of Accounting Standards Update 2018-02 (Note 1)	$ 4,000,000
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Provision for (benefit from) income taxes		$ (5,000,000)

Business Acquisition - Provisio

Business Acquisition - Provisional Purchase Price for Acquisition (Detail) - Scottrade [Member] $ / shares in Units, $ in Millions	Sep. 18, 2017USD ($)$ / sharesshares
Business Acquisition [Line Items]
TD Ameritrade Holding Corporation common stock issued to the Riney Stockholder and the Escrow Account	$ 1,261
Cash paid at closing	3,073
Total purchase price	4,334
Bank merger consideration amount paid by TD Bank, NA to Scottrade	$ 1,370
Riney Stockholder [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Equity interests issued in connection with the acquisition, number of shares, total | shares	27,685,493
Equity interests issued in connection with the acquisition, share price (in dollars per share) | $ / shares	$ 45.55

Business Acquisition - Provis_2

Business Acquisition - Provisional Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Sep. 18, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Goodwill	$ 4,227	$ 4,213		$ 2,467
Scottrade [Member]
Business Acquisition [Line Items]
Cash and cash equivalents			$ 1,785
Cash and investments segregated and on deposit for regulatory purposes			3,535
Receivable from brokers and dealers and clearing organizations			167
Receivable from clients, net			3,136
Receivable from affiliates			2
Other receivables			54
Securities owned			37
Property and equipment			136
Goodwill			1,760
Acquired intangible assets			974
Deferred tax assets			70
Other assets			35
Total assets acquired			11,691
Payable to brokers and dealers and clearing organizations			(354)
Payable to clients			(6,248)
Accounts payable and other liabilities			(272)
Payable to affiliates			(47)
Long-term debt			(436)
Total liabilities assumed			(7,357)
Total provisional purchase price allocated			4,334
Bank merger consideration amount paid by TD Bank, NA to Scottrade, included in Cash and cash equivalents			$ 1,370
Scottrade [Member] | Senior Notes [Member] | 6.125% Senior Notes [Member]
Business Acquisition [Line Items]
Interest rate, stated percentage, related to Scottrade long-term debt acquired			6.125%
Scottrade [Member] | Secured Debt [Member] | 6.18% Secured Loan [Member]
Business Acquisition [Line Items]
Interest rate, stated percentage, related to Scottrade long-term debt acquired			6.18%

Business Acquisition - Pro Form

Business Acquisition - Pro Forma Financial Information (Unaudited) (Detail) - Scottrade [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Pro Forma Financial Information (Unaudited):
Pro forma net revenues	$ 4,586	$ 4,158
Pro forma net income	$ 921	$ 700
Pro forma basic earnings per share	$ 1.62	$ 1.23
Pro forma diluted earnings per share	$ 1.62	$ 1.22

Business Acquisition - Addition

Business Acquisition - Additional Information (Detail) $ / shares in Units, $ in Millions	Sep. 18, 2017USD ($)branch$ / sharesshares	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Business Acquisition [Line Items]
Stock issued, value of shares											$ 400
Purchase accounting adjustments, reduction to goodwill										$ (14)
Actual net revenues		$ 1,398	$ 1,382	$ 1,415	$ 1,257	$ 983	$ 931	$ 904	$ 859	5,452	3,676	$ 3,327
Actual net loss		$ 454	$ 451	$ 271	$ 297	$ 211	$ 231	$ 214	$ 216	$ 1,473	$ 872	$ 842
Senior Notes [Member] | 3.300% Notes due 2027 [Member]
Business Acquisition [Line Items]
Interest rate, stated percentage		3.30%				3.30%				3.30%	3.30%
Scottrade [Member]
Business Acquisition [Line Items]
Approximate number of branch locations acquired | branch	500
Bank merger consideration amount paid by TD Bank, NA to Scottrade	$ 1,370
Cash paid at acquisition closing, subject to closing adjustments	3,073
Purchase accounting adjustments, reduction to goodwill										$ 14
Goodwill associated with the Acquisition, expected to be deductible for income tax purposes	$ 1,630
Scottrade [Member] | TD [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Stock issued, number of shares (in shares) | shares	11,074,197
Stock issued, price per share (in dollars per share) | $ / shares	$ 36.12
Stock issued, value of shares	$ 400
Scottrade [Member] | Riney Stockholder [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Equity interests issued in connection with the acquisition, number of shares, total | shares	27,685,493
Equity interests issued in connection with the acquisition, number of shares, shares deposited in escrow | shares	1,736,815

Cash and Cash Equivalents - Sum

Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 2,690	$ 1,472	$ 1,855	$ 1,978
Broker-dealer subsidiaries [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	2,094	997
Corporate [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	342	279
Trust company subsidiary [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	124	79
Futures commission merchant and forex dealer member subsidiary [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	89	98
Investment advisory subsidiaries [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 41	$ 19

Cash and Investments Segregat_3

Cash and Investments Segregated and on Deposit for Regulatory Purposes (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and investments segregated and on deposit for regulatory purposes	$ 3,185	$ 10,446
U.S. Government Agency Mortgage-Backed Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and investments segregated and on deposit for regulatory purposes	1,302	1,486
Cash in Demand Deposit Accounts [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and investments segregated and on deposit for regulatory purposes	956	3,653
Reverse Repurchase Agreements (collateralized by U.S. government debt securities) [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and investments segregated and on deposit for regulatory purposes	500	1,004
Cash on Deposit with Futures Commission Merchants [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and investments segregated and on deposit for regulatory purposes	202	209
U.S. Government Debt Securities [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and investments segregated and on deposit for regulatory purposes	200	4,019
U.S. Government Debt Securities on Deposit with Futures Commission Merchant [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and investments segregated and on deposit for regulatory purposes	$ 25	$ 75

Receivable from and Payable t_3

Receivable from and Payable to Brokers, Dealers and Clearing Organizations - Amounts Receivable from and Payable to Brokers, Dealers and Clearing Organizations (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Receivable:
Deposits paid for securities borrowed	$ 803	$ 1,154
Clearing organizations	545	151
Broker-dealers	14	21
Securities failed to deliver	12	8
Total	1,374	1,334
Payable:
Deposits received for securities loaned	2,914	2,449
Securities failed to receive	34	21
Clearing organizations	29	32
Broker-dealers	3	2
Total	$ 2,980	$ 2,504

Allowance for Doubtful Accoun_3

Allowance for Doubtful Accounts on Client and Other Receivables (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning balance	$ 11	$ 9	$ 12
Provision for doubtful accounts on client and other receivables	56	2	2
Acquired in business acquisition	0	2	0
Write-off of doubtful accounts	(13)	(2)	(5)
Ending balance	$ 54	$ 11	$ 9

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,295	$ 1,270
Less: Accumulated depreciation and amortization	(503)	(518)
Property and equipment at cost, net	792	752
Building and building components [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	462	351
Computer equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	326	270
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	178	215
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	176	173
Building construction in process [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	0	101
Land [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	61	77
Other property and equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 92	$ 83

Goodwill and Acquired Intangi_3

Goodwill and Acquired Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 4,213	$ 2,467
Goodwill recorded in acquisition of Scottrade (see Note 2)		1,746
Purchase accounting adjustments	14
Goodwill, ending balance	$ 4,227	$ 4,213

Goodwill and Acquired Intangi_4

Goodwill and Acquired Intangible Assets - Acquired Intangible Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Acquired Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,447	$ 2,447
Accumulated Amortization	(1,118)	(977)
Net Carrying Amount	1,329	1,470
Trade names [Member]
Acquired Intangible Assets [Line Items]
Gross Carrying Amount	10	10
Accumulated Amortization	(7)	0
Net Carrying Amount	3	10
Trademark license [Member]
Acquired Intangible Assets [Line Items]
Gross Carrying Amount	146	146
Accumulated Amortization	0	0
Net Carrying Amount	146	146
Client relationships [Member]
Acquired Intangible Assets [Line Items]
Gross Carrying Amount	2,183	2,183
Accumulated Amortization	(1,003)	(877)
Net Carrying Amount	1,180	1,306
Technology and content [Member]
Acquired Intangible Assets [Line Items]
Gross Carrying Amount	108	108
Accumulated Amortization	(108)	(100)
Net Carrying Amount	$ 0	$ 8

Goodwill and Acquired Intangi_5

Goodwill and Acquired Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense on acquired intangible assets	$ 141	$ 79	$ 86

Goodwill and Acquired Intangi_6

Goodwill and Acquired Intangible Assets - Estimated Future Amortization Expense for Acquired Intangible Assets (Detail) $ in Millions	Sep. 30, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2,019	$ 124
2,020	116
2,021	106
2,022	105
2,023	75
Thereafter (to 2035)	657
Total	$ 1,183

Exit Liabilities - Summary of t

Exit Liabilities - Summary of the Activity in Exit Liabilities (Detail) - Scottrade [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Restructuring Reserve [Roll Forward]
Beginning balance	$ 138	$ 4
Exit liabilities assumed in business acquisition	9	100
Costs incurred and charged to expense	448	44
Costs paid or otherwise settled	(526)	(10)
Ending balance	69	138
Employee Compensation and Benefits [Member]
Restructuring Reserve [Roll Forward]
Beginning balance	138	4
Exit liabilities assumed in business acquisition	0	100
Costs incurred and charged to expense	235	43
Costs paid or otherwise settled	(352)	(9)
Ending balance	21	138
Other [Member]
Restructuring Reserve [Roll Forward]
Beginning balance	0	0
Exit liabilities assumed in business acquisition	9	0
Costs incurred and charged to expense	213	1
Costs paid or otherwise settled	(174)	(1)
Ending balance	$ 48	$ 0

Exit Liabilities - Summary of_2

Exit Liabilities - Summary of the Cumulative Acquisition-Related Exit Costs (Detail) - Scottrade [Member] $ in Millions	12 Months Ended
	Sep. 30, 2018USD ($)
Restructuring Cost and Reserve [Line Items]
Exit liabilities assumed in business acquisition	$ 109
Total cumulative exit liabilities assumed and acquisition-related exit costs incurred	590
Employee Severance and Other Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Exit liabilities assumed in business acquisition	100
Total cumulative exit liabilities assumed and acquisition-related exit costs incurred	367
Contract Termination and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Exit liabilities assumed in business acquisition	9
Total cumulative exit liabilities assumed and acquisition-related exit costs incurred	223
Employee Compensation and Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	267
Employee Compensation and Benefits [Member] | Employee Severance and Other Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	267
Employee Compensation and Benefits [Member] | Contract Termination and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	0
Clearing And Execution Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	1
Clearing And Execution Costs [Member] | Employee Severance and Other Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	0
Clearing And Execution Costs [Member] | Contract Termination and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	1
Communications [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	1
Communications [Member] | Employee Severance and Other Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	0
Communications [Member] | Contract Termination and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	1
Occupancy and Equipment Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	7
Occupancy and Equipment Costs [Member] | Employee Severance and Other Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	0
Occupancy and Equipment Costs [Member] | Contract Termination and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	7
Professional Services [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	30
Professional Services [Member] | Employee Severance and Other Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	0
Professional Services [Member] | Contract Termination and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	30
Other Operating Income (Expense) [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	173
Other Operating Income (Expense) [Member] | Employee Severance and Other Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	0
Other Operating Income (Expense) [Member] | Contract Termination and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	173
Other Nonoperating Income (Expense) [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	2
Other Nonoperating Income (Expense) [Member] | Employee Severance and Other Termination Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	0
Other Nonoperating Income (Expense) [Member] | Contract Termination and Other Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cumulative acquisition-related exit costs incurred since the date of acquisition	$ 2

Exit Liabilities - Additional I

Exit Liabilities - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Series of Individually Immaterial Business Acquisitions [Member]
Restructuring Cost and Reserve [Line Items]
Exit liabilities recorded during the period	$ 0	$ 0	$ 0

Long-term Debt and Other Borr_3

Long-term Debt and Other Borrowings - Schedule of Long-term Debt and Other Borrowings (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Oct. 17, 2014
Debt Instrument [Line Items]
Face Value	$ 2,646	$ 2,647
Unamortized Discounts and Debt Issuance Costs	(17)	(18)
Fair Value Adjustment	(94)	23
Net Carrying Value	2,535	2,652
Senior Notes [Member]
Debt Instrument [Line Items]
Face Value	2,550	2,550
Unamortized Discounts and Debt Issuance Costs	(17)	(18)
Fair Value Adjustment	(94)	23
Net Carrying Value	$ 2,439	2,555
Senior Notes [Member] | 5.600% Notes due 2019 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	5.60%
Face Value	$ 500	500
Unamortized Discounts and Debt Issuance Costs	(1)	(1)
Fair Value Adjustment	2	15
Net Carrying Value	$ 501	514
Senior Notes [Member] | 2.950% Notes due 2022 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	2.95%
Face Value	$ 750	750
Unamortized Discounts and Debt Issuance Costs	(4)	(5)
Fair Value Adjustment	(27)	0
Net Carrying Value	$ 719	745
Senior Notes [Member] | 3.625% Notes due 2025 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	3.625%
Face Value	$ 500	500	$ 500
Unamortized Discounts and Debt Issuance Costs	(3)	(3)
Fair Value Adjustment	(17)	11
Net Carrying Value	$ 480	$ 508
Senior Notes [Member] | 3.300% Notes due 2027 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	3.30%	3.30%
Face Value	$ 800	$ 800
Unamortized Discounts and Debt Issuance Costs	(9)	(9)
Fair Value Adjustment	(52)	(3)
Net Carrying Value	739	788
Securities Sold Under Agreements to Repurchase [Member]
Debt Instrument [Line Items]
Face Value	96	97
Unamortized Discounts and Debt Issuance Costs	0	0
Fair Value Adjustment	0	0
Net Carrying Value	$ 96	$ 97

Long-term Debt and Other Borr_4

Long-term Debt and Other Borrowings - Fiscal Year Maturities on Long-term Debt Outstanding (Detail) $ in Millions	Sep. 30, 2018USD ($)
Debt Disclosure [Abstract]
2,019	$ 0
2,020	500
2,021	0
2,022	750
2,023	0
Thereafter	1,300
Total	$ 2,550

Long-term Debt and Other Borr_5

Long-term Debt and Other Borrowings - Key Information Of Senior Notes and Lines of Credit (Detail) - USD ($) $ in Millions	Oct. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Oct. 17, 2014
Debt Instrument [Line Items]
Aggregate Principal		$ 2,646	$ 2,647
Senior Notes [Member]
Debt Instrument [Line Items]
Aggregate Principal		2,550	2,550
Senior Notes [Member] | 2019 Notes [Member]
Debt Instrument [Line Items]
Aggregate Principal		$ 500	500
Interest rate, stated percentage		5.60%
Senior Notes [Member] | 2.950% Notes due 2022 [Member]
Debt Instrument [Line Items]
Aggregate Principal		$ 750	750
Interest rate, stated percentage		2.95%
Senior Notes [Member] | 2025 Notes [Member]
Debt Instrument [Line Items]
Aggregate Principal		$ 500	500	$ 500
Interest rate, stated percentage		3.625%
Senior Notes [Member] | 2027 Notes [Member]
Debt Instrument [Line Items]
Aggregate Principal		$ 800	$ 800
Interest rate, stated percentage		3.30%	3.30%
Subsequent Event [Member] | Senior Notes [Member] | 2021 Notes [Member]
Debt Instrument [Line Items]
Aggregate Principal	$ 600
Subsequent Event [Member] | Senior Notes [Member] | 2024 Notes [Member]
Debt Instrument [Line Items]
Aggregate Principal	$ 400
Interest rate, stated percentage	3.75%
TD Ameritrade Clearing, Inc [Member] | Committed Intercompany Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity		$ 400
TD Ameritrade Clearing, Inc [Member] | Uncommitted Intercompany Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity		300
TD Ameritrade, Inc [Member] | Uncommitted Intercompany Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity		300
TD Ameritrade Futures & Forex LLC [Member] | Committed Intercompany Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity		$ 45

Long-term Debt and Other Borr_6

Long-term Debt and Other Borrowings - Senior Notes, Securities Sold Under Agreements to Repurchase and Secured Loan - Additional Information (Detail)	Oct. 30, 2018USD ($)	Sep. 30, 2018USD ($)bank	Sep. 30, 2017USD ($)	Oct. 17, 2014USD ($)
Debt Instrument [Line Items]
Borrowings outstanding		$ 2,535,000,000	$ 2,652,000,000
Debt instrument, face value		2,646,000,000	2,647,000,000
Securities Sold Under Agreements to Repurchase [Member]
Debt Instrument [Line Items]
Borrowings outstanding		96,000,000	97,000,000
Debt instrument, face value		$ 96,000,000	$ 97,000,000
Debt instrument, effective interest rate		2.35%	1.25%
Senior Notes [Member]
Debt Instrument [Line Items]
Borrowings outstanding		$ 2,439,000,000	$ 2,555,000,000
Debt instrument, face value		2,550,000,000	2,550,000,000
Senior Notes [Member] | 5.600% Notes due 2019 [Member]
Debt Instrument [Line Items]
Borrowings outstanding		501,000,000	514,000,000
Debt instrument, face value		$ 500,000,000	500,000,000
Interest rate, stated percentage		5.60%
Debt instrument, redemption price, percentage		100.00%
Debt instrument, redemption price, basis spread added to U.S. Treasury rate		0.35%
Senior Notes [Member] | Senior Notes Due 2022, 2025 and 2027 [Member] | Time period prior to specified redemption date [Member]
Debt Instrument [Line Items]
Debt instrument, redemption price, percentage		100.00%
Senior Notes [Member] | Senior Notes Due 2022, 2025 and 2027 [Member] | Time period on or after specified redemption date [Member]
Debt Instrument [Line Items]
Debt instrument, redemption price, percentage		100.00%
Senior Notes [Member] | 2.950% Notes due 2022 [Member]
Debt Instrument [Line Items]
Borrowings outstanding		$ 719,000,000	745,000,000
Debt instrument, face value		$ 750,000,000	750,000,000
Interest rate, stated percentage		2.95%
Senior Notes [Member] | 2.950% Notes due 2022 [Member] | Time period prior to specified redemption date [Member]
Debt Instrument [Line Items]
Debt instrument, redemption price, basis spread added to U.S. Treasury rate		0.15%
Senior Notes [Member] | 3.625% Notes due 2025 [Member]
Debt Instrument [Line Items]
Borrowings outstanding		$ 480,000,000	508,000,000
Debt instrument, face value		$ 500,000,000	500,000,000	$ 500,000,000
Interest rate, stated percentage		3.625%
Senior Notes [Member] | 3.625% Notes due 2025 [Member] | Time period prior to specified redemption date [Member]
Debt Instrument [Line Items]
Debt instrument, redemption price, basis spread added to U.S. Treasury rate		0.25%
Senior Notes [Member] | 3.300% Notes due 2027 [Member]
Debt Instrument [Line Items]
Borrowings outstanding		$ 739,000,000	788,000,000
Debt instrument, face value		$ 800,000,000	$ 800,000,000
Interest rate, stated percentage		3.30%	3.30%
Senior Notes [Member] | 3.300% Notes due 2027 [Member] | Time period prior to specified redemption date [Member]
Debt Instrument [Line Items]
Debt instrument, redemption price, basis spread added to U.S. Treasury rate		0.20%
Subsequent Event [Member] | Senior Notes [Member] | Senior Notes Due 2021 And 2024 [Member]
Debt Instrument [Line Items]
Debt instrument, face value	$ 1,000,000,000
Debt instrument, redemption price, percentage	100.00%
TD Ameritrade Clearing, Inc [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Number of unaffiliated banks | bank		2
Borrowings outstanding		$ 0

Long-term Debt and Other Borr_7

Long-term Debt and Other Borrowings - Fair Value Hedging - Additional Information (Detail) - Senior Notes [Member]	12 Months Ended
	Sep. 30, 2018
2019, 2022, 2025 and 2027 Senior Notes [Member]
Debt Instrument [Line Items]
Weighted-average effective interest rate	3.62%
2019, 2022, 2025 and 2027 Senior Notes [Member] | LIBOR [Member] | Pay Variable Interest Rate Swap [Member]
Debt Instrument [Line Items]
Debt instrument, description of basis spread on variable rate	three-month LIBOR
5.600% Notes due 2019 [Member] | LIBOR [Member] | Pay Variable Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, basis spread on variable rate, percentage	2.3745%
2.950% Notes due 2022 [Member] | LIBOR [Member] | Pay Variable Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, basis spread on variable rate, percentage	0.9486%
3.625% Notes due 2025 [Member] | LIBOR [Member] | Pay Variable Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, basis spread on variable rate, percentage	1.1022%
3.300% Notes due 2027 [Member] | LIBOR [Member] | Pay Variable Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, basis spread on variable rate, percentage	1.034%

Long-term Debt and Other Borr_8

Long-term Debt and Other Borrowings - Gains and Losses Resulting from Changes in Fair Value of Interest Rate Swaps and Hedged Fixed Rate Debt (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Debt Disclosure [Abstract]
Gain (loss) on fair value of interest rate swaps	$ (117)	$ (56)	$ 16
Gain (loss) on fair value of hedged fixed-rate debt	117	56	(16)
Net gain (loss) recorded in interest on borrowings	$ 0	$ 0	$ 0

Long-term Debt and Other Borr_9

Long-term Debt and Other Borrowings - Cash Flow Hedging - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Oct. 17, 2014	Jan. 17, 2014
Debt Instrument [Line Items]
Debt instrument, face value	$ 2,646	$ 2,647
Forward Starting Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, notional amount				$ 500
Derivative, amount paid to settle contract			$ 45
Amount of interest rate cash flow hedge gain (loss) to be reclassified during next 12 months, net	(4.4)
Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face value	2,550	2,550
Senior Notes [Member] | 3.625% Notes due 2025 [Member]
Debt Instrument [Line Items]
Debt instrument, face value	$ 500	$ 500	$ 500

Long-term Debt and Other Bor_10

Long-term Debt and Other Borrowings - Fair Value of Outstanding Derivatives Designated as Hedging Instruments (Detail) - Pay Variable Interest Rate Swap [Member] - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Other assets [Member]
Derivatives, Fair Value [Line Items]
Fair value of outstanding derivative assets designated as hedging instruments in the Consolidated Balance Sheets	$ 2	$ 26
Accounts payable and other liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value of outstanding derivative liabilities designated as hedging instruments in the Consolidated Balance Sheets	$ (96)	$ (3)

Long-term Debt and Other Bor_11

Long-term Debt and Other Borrowings - Balance Sheet Impact of Hedging Instruments - Additional Information (Details) - Pay Variable Interest Rate Swap [Member] - Cash [Member] - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Debt Instrument [Line Items]
Pledged collateral from interest rate swap counterparty, aggregate fair value	$ 10	$ 40
Pledged collateral to interest rate swap counterparty, aggregate fair value	$ 82	$ 1

Long-term Debt and Other Bor_12

Long-term Debt and Other Borrowings - Credit Agreements - Additional Information (Detail)	Apr. 21, 2017USD ($)facility	Jun. 30, 2018	Sep. 30, 2018USD ($)	Feb. 16, 2018USD ($)	Sep. 30, 2017USD ($)
Intercompany Credit Agreements [Member]
Debt Instrument [Line Items]
Notes payable, borrowings outstanding			$ 0		$ 0
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	$ 300,000,000		$ 300,000,000
Credit facility, commitment fee percentage			0.125%
Notes payable, borrowings outstanding			$ 0		0
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Credit facility, commitment fee percentage			0.08%
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Credit facility, commitment fee percentage			0.20%
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | Eurodollar Loans [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.125%
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | Eurodollar Loans [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.875%
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | Eurodollar Loans [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.50%
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | ABR Loans [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.125%
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | ABR Loans [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.00%
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | ABR Loans [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.50%
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | ABR Loans [Member] | Federal Funds Effective Rate [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.50%
TD Ameritrade Holding Corporation [Member] | Senior Unsecured Revolving Credit Facility [Member] | ABR Loans [Member] | Eurodollar [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.00%
TD Ameritrade Holding Corporation [Member] | February 2018 Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity				$ 500,000,000
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	$ 1,450,000,000		$ 600,000,000
Number of credit facilities | facility	2
Notes payable, borrowings outstanding			$ 0		0
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
Credit facility, commitment fee percentage			0.07%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Credit facility, commitment fee percentage			0.175%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Eurodollar Loans [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.75%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Eurodollar Loans [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.25%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Federal Funds Rate Loans [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.00%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Federal Funds Rate Loans [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			0.75%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Federal Funds Rate Loans [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate			1.25%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Revolving Facility, 600 Million Dollars [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	$ 600,000,000
Credit facility, commitment fee percentage		0.10%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Revolving Facility, 850 Million Dollars [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	$ 850,000,000
Credit facility, commitment fee percentage		0.08%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Revolving Facility, 850 Million Dollars [Member] | Minimum [Member]
Debt Instrument [Line Items]
Credit facility, commitment fee percentage	0.06%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | Revolving Facility, 850 Million Dollars [Member] | Maximum [Member]
Debt Instrument [Line Items]
Credit facility, commitment fee percentage	0.125%
TD Ameritrade Clearing, Inc [Member] | Senior Unsecured Revolving Credit Facility [Member] | TDAC Eurodollar Loans [Member] | LIBOR [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		1.00%
TD Ameritrade Clearing, Inc [Member] | Committed Intercompany Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity			$ 400,000,000
TD Ameritrade Clearing, Inc [Member] | Uncommitted Intercompany Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity			300,000,000
TD Ameritrade Holding Corporation and TD Ameritrade Clearing, Inc. [Member] | Senior Revolving Credit Facilities [Member]
Debt Instrument [Line Items]
Lending Commitment Received From Related Party			$ 257,000,000		$ 115,000,000

Income Taxes - Provision for In

Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Current expense (benefit):
Federal	$ 380	$ 484	$ 435
State	58	49	(4)
Total	438	533	431
Deferred expense (benefit):
Federal	(32)	(11)	(5)
State	8	0	(3)
Total	(24)	(11)	(8)
Provision for income taxes	$ 414	$ 522	$ 423

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Federal Statutory Tax Rate to Effective Tax Rate (Detail)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	24.50%	35.00%	35.00%
Statutory versus actual blended federal income tax rate	(1.30%)	0.00%	0.00%
State taxes, net of federal tax effect	2.60%	2.80%	2.80%
Adjustments to estimated state income taxes	0.00%	0.00%	(0.20%)
Federal incentives	0.40%	(0.30%)	(1.40%)
Interest recorded (reversed) on unrecognized tax benefits, net	0.20%	0.20%	(1.10%)
Remeasurement of U.S. deferred income taxes	(3.80%)	0.00%	0.00%
Reversal of accruals for unrecognized tax benefits	(0.40%)	(0.40%)	(1.80%)
Share-based payment compensation	(0.30%)	0.00%	0.00%
Other	0.00%	0.10%	0.10%
Effective income tax rate	21.90%	37.40%	33.40%

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets (Liabilities) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Deferred tax assets:
Accrued and other liabilities	$ 78	$ 131
Stock-based compensation	19	28
Allowance for doubtful accounts	14	6
Unrecognized loss on cash flow hedging instruments	9	15
Intangible assets, state tax benefit	3	5
Operating loss carryforwards	2	1
Gross deferred tax assets	125	186
Less: Valuation allowance	(2)	(1)
Net deferred tax assets	123	185
Deferred tax liabilities:
Acquired intangible assets	(236)	(331)
Property and equipment	(46)	(35)
Prepaid expenses	(13)	(11)
Unrealized gain on investments	(2)	0
Other deferred tax liabilities	(3)	(1)
Total deferred tax liabilities	(300)	(378)
Net deferred tax liabilities	$ (177)	$ (193)

Income Taxes - Reconciliation_2

Income Taxes - Reconciliation of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 152	$ 142	$ 154
Additions based on tax positions related to the current year	35	28	30
Additions for tax positions of prior years	8	0	20
Reductions due to lapsed statute of limitations	(9)	(7)	(8)
Reductions due to settlements with taxing authorities	(3)	(1)	(21)
Reductions for tax positions of prior years	(2)	(10)	(33)
Ending balance	$ 181	$ 152	$ 142

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Taxes [Line Items]
Federal statutory income tax rate	24.50%	35.00%	35.00%
Effective income tax rate	21.90%	37.40%	33.40%
Net favorable remeasurement of deferred income tax balances from tax reform	$ 71
Net favorable change from equity-based compensation ASU 2016-09	5
Net favorable resolutions of state income tax matters	12	$ 8
Favorable deduction from acquisition-related exit costs	$ 30
Net favorable per share impact on earnings	$ 0.19	$ 0.02	$ 0.12
Net favorable impact from federal incentives	$ (9)	$ 4	$ 18
Net favorable adjustments to uncertain tax positions and related deferred income tax assets			39
Favorable tax liability remeasurement related to a state court decision			33
Net favorable deferred income tax adjustments			5
Subsidiaries state operating loss carryforwards	35
Unrecognized tax benefits	181	152	142	$ 154
Unrecognized tax benefits net of federal benefit on state matters that would Impact effective tax rate	$ 151	108
Statute of limitations from the date the tax return is filed, minimum	3 years
Statute of limitations from the date the tax return is filed, minimum	4 years
Reasonably possible reduction in unrecognized tax benefits	$ 77
Reasonably possible reduction in unrecognized tax benefits net of federal benefit on state matters	67
Interest and penalties expense (benefit) recognized	4	2	$ (17)
Accrued interest and penalties related to unrecognized tax benefits	$ 30	$ 26

Capital Requirements - Net Capi

Capital Requirements - Net Capital and Net Capital Requirements for Company's Subsidiaries (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
TD Ameritrade Clearing, Inc [Member]
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
Net Capital	$ 2,831,000	$ 1,595,000
Required Net Capital (2% of Aggregate Debit Balances)	525,000	340,000
Net Capital in Excess of Required Net Capital	$ 2,306,000	$ 1,255,000
Ratio of Net Capital to Aggregate Debit Balances	10.79%	9.39%
TD Ameritrade, Inc [Member]
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
Net Capital	$ 181,000	$ 155,000
Required Net Capital (Minimum Dollar Requirement)	250	250
Net Capital in Excess of Required Net Capital	181,000	155,000
Scottrade [Member]
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
Net Capital		348,000
Required Net Capital (2% of Aggregate Debit Balances)		70,000
Net Capital in Excess of Required Net Capital		$ 278,000
Ratio of Net Capital to Aggregate Debit Balances		9.99%
TD Ameritrade Futures & Forex LLC [Member]
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
Adjusted Net Capital under Commodity Exchange Act	129,000	$ 77,000
Required Adjusted Net Capital under Commodity Exchange Act	23,000	22,000
Adjusted Net Capital in Excess of Required Adjusted Net Capital	$ 106,000	$ 55,000

Capital Requirements - Addition

Capital Requirements - Additional Information (Detail) - USD ($)	Sep. 30, 2018	Sep. 30, 2017
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
Alternative net capital requirement, percentage of net capital to aggregate debit balances required for a broker-dealer to repay subordinated borrowings, pay cash dividends, or make any unsecured advances or loans to its parent company or employees	5.00%
Alternative net capital requirement, percentage of net capital to the minimum dollar requirement required for a broker-dealer to repay subordinated borrowings, pay cash dividends, or make any unsecured advances or loans to its parent company or employees	120.00%
TD Ameritrade Clearing, Inc [Member]
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
Alternative net capital requirement, dollar amount threshold	$ 1,500,000
Alternative net capital requirement, percentage of aggregate debit balances	2.00%
TD Ameritrade, Inc [Member]
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
Alternative net capital requirement, dollar amount threshold	$ 250,000
Alternative net capital requirement, percentage of aggregate debit balances	2.00%
Scottrade [Member]
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
Alternative net capital requirement, dollar amount threshold		$ 250,000
Alternative net capital requirement, percentage of aggregate debit balances		2.00%
TD Ameritrade Futures & Forex LLC [Member]
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
FCM required net capital under the Commodity Exchange Act, dollar amount threshold	$ 1,000,000
FCM required net capital under the Commodity Exchange Act, percentage of total risk margin requirement for all positions carried in client accounts	8.00%
FCM required net capital under the Commodity Exchange Act, percentage of total risk margin requirements for all positions carried in non-client accounts	8.00%
FDM required net capital under the Commodity Exchange Act, dollar amount threshold	$ 20,000,000
FDM required net capital under the Commodity Exchange Act, percentage of forex liabilities in excess of $10 million added to the dollar amount threshold	5.00%
FDM required net capital under the Commodity Exchange Act, minimum forex client liability dollar amount threshold	$ 10,000,000
FCM and FDM required net capital under the Commodity Exchange Act, required notice to CFTC, minimum percentage of adjusted net capital to the risk-based capital requirement	110.00%
FCM and FDM required net capital under the Commodity Exchange Act, required notice to CFTC, minimum percentage of adjusted net capital to the FCM's $1 million threshold	150.00%
FCM and FDM required net capital under the Commodity Exchange Act, required notice to CFTC, minimum percentage of adjusted net capital to the FDM's $20 million plus 5% of foreign exchange liabilities owed to forex clients in excess of $10 million threshold	110.00%
TD Ameritrade Trust Company [Member]
Net Capital and Net Capital Requirements For Company's Subsidiaries [Line Items]
Tier 1 capital, balance at period end	$ 39,000,000	$ 32,000,000
Amount in excess of required Tier 1 capital	$ 18,000,000	$ 13,000,000

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Option Activity in Stock Incentive Plans (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Number of Options [Roll Forward]
Number of Options, Outstanding at beginning of year (in shares)	503
Number of Options, Outstanding at end of year (in shares)	503
Number of Options, Exercisable at end of year (in shares)	252
Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Outstanding at beginning of year (in dollars per share)	$ 27.97
Weighted Average Exercise Price, Outstanding at end of year (in dollars per share)	27.97
Weighted Average Exercise Price, Exercisable at end of year (in dollars per share)	$ 27.97
Weighted Average Remaining Contractual Term, Outstanding at beginning and end of year	7 years 3 months 18 days
Weighted Average Remaining Contractual Term, Exercisable at end of year	7 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding at end of year	$ 13	$ 13
Aggregate Intrinsic Value, Exercisable at end of year	$ 6

Stock-based Compensation - Assu

Stock-based Compensation - Assumptions for Estimation of Fair Value of Awards Granted (Details)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate			1.73%
Expected dividend yield			2.40%
Expected volatility			27.00%
Expected term (years)			6 years 6 months
PRSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.84%	1.34%
Expected dividend yield	0.00%	0.00%
Expected volatility	28.00%	27.00%
Expected term (years)	2 years 9 months 18 days	2 years 10 months 24 days

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Restricted Stock Unit and Performance Restricted Stock Unit Activity in Stock Incentive Plans (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
RSUs [Member]
Number of Units [Roll Forward]
Number of Units, Nonvested at beginning of year (in shares)	2,394,000
Number of Units, Granted (in shares)	671,000
Number of Units, Vested (in shares)	(807,000)
Number of Units, Forfeited (in shares)	(129,000)
Number of Units, Nonvested at end of year (in shares)	2,129,000	2,394,000
Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value, Nonvested at beginning of year (in dollars per share)	$ 34.83
Weighted Average Grant Date Fair Value, Granted (in dollars per share)	50.61	$ 40.66	$ 27.97
Weighted Average Grant Date Fair Value, Vested (in dollars per share)	33.24
Weighted Average Grant Date Fair Value, Forfeited (in dollars per share)	41.72
Weighted Average Grant Date Fair Value, Nonvested at end of year (in dollars per share)	$ 39.99	$ 34.83
PRSUs [Member]
Number of Units [Roll Forward]
Number of Units, Nonvested at beginning of year (in shares)	265,000
Number of Units, Granted (in shares)	235,000		0
Number of Units, Nonvested at end of year (in shares)	500,000	265,000
Weighted Average Grant Date Fair Value [Abstract]
Weighted Average Grant Date Fair Value, Nonvested at beginning of year (in dollars per share)	$ 39.48
Weighted Average Grant Date Fair Value, Granted (in dollars per share)	49.50	$ 39.48
Weighted Average Grant Date Fair Value, Nonvested at end of year (in dollars per share)	$ 44.19	$ 39.48

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2018USD ($)stock_incentive_plan$ / sharesshares	Sep. 30, 2017USD ($)$ / shares	Sep. 30, 2016USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock incentive plans | stock_incentive_plan	2
Stock-based compensation expense	$ 60	$ 36	$ 34
Stock-based compensation expense, income tax benefits	$ 17	14	$ 13
Options exercised (in shares) | shares	0
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period from grant date	10 years
Weighted-average grant date fair value of options granted (in dollars per share) | $ / shares			$ 6.16
Number of options granted during period (in shares) | shares	0
Total intrinsic value of options exercised during period		$ 26	$ 0.1
Unrecognized compensation costs related to nonvested awards, options	$ 1
Weighted average period of recognition for unrecognized compensation costs related to nonvested awards	1 year 3 months 21 days
Expected dividend yield			2.40%
Stock Options [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Stock Options [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value of awards other than options granted during the period (in dollars per share) | $ / shares	$ 50.61	$ 40.66	$ 27.97
Unrecognized compensation costs related to nonvested awards, awards other than options	$ 31
Weighted average period of recognition for unrecognized compensation costs related to nonvested awards	1 year 10 months 24 days
Fair value of awards other than options vested during period	$ 42	$ 70	$ 71
Number of awards other than options granted during the period (in shares) | shares	671,000
RSUs [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
RSUs [Member] | Non-employee Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
PRSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Weighted-average grant-date fair value of awards other than options granted during the period (in dollars per share) | $ / shares	$ 49.50	$ 39.48
Unrecognized compensation costs related to nonvested awards, awards other than options	$ 9
Weighted average period of recognition for unrecognized compensation costs related to nonvested awards	1 year 10 months 13 days
Number of awards other than options granted during the period (in shares) | shares	235,000		0
Expected dividend yield	0.00%	0.00%
PRSUs [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target percentage range related to number of shares of common stock issued	80.00%
PRSUs [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target percentage range related to number of shares of common stock issued	120.00%
Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for issuance to eligible employees, consultants and non-employee directors (in shares) | shares	42,104,174
2006 Directors Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for issuance to eligible employees, consultants and non-employee directors (in shares) | shares	1,830,793

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Retirement Benefits [Abstract]
Profit-sharing and matching contributions expense	$ 53	$ 38	$ 35

Commitments and Contingencies -

Commitments and Contingencies - Future Minimum Rental Commitments Under Non-Cancelable Operating Leases (Detail) $ in Millions	Sep. 30, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Minimum Lease Payments 2019	$ 75
Minimum Lease Payments 2020	64
Minimum Lease Payments 2021	45
Minimum Lease Payments 2022	34
Minimum Lease Payments 2023	28
Minimum Lease Payments Thereafter (to 2033)	99
Total Minimum Lease Payments	345
Sublease Income 2019	(1)
Sublease Income 2020	(1)
Sublease Income 2021	0
Sublease Income 2022	0
Sublease Income 2023	0
Sublease Income Thereafter (to 2033)	0
Total Sublease Income	(2)
Net Lease Commitments 2019	74
Net Lease Commitments 2020	63
Net Lease Commitments 2021	45
Net Lease Commitments 2022	34
Net Lease Commitments 2023	28
Net Lease Commitments Thereafter (to 2033)	99
Total Net Lease Commitments	$ 343

Commitments and Contingencies_2

Commitments and Contingencies - Collateral Available, Loaned or Repledged (Detail) - USD ($) $ in Billions	Sep. 30, 2018	Sep. 30, 2017
Customer Securities for which Entity has Right to Sell or Repledge (Including Securities Sold or Repledged) [Line Items]
Total collateral available	$ 32.2	$ 25
Total collateral loaned or repledged, collateral loaned	2.9	2.4
Total collateral loaned or repledged, collateral repledged	6.3	4.1
Total collateral loaned or repledged	9.2	6.5
Client Margin Securities [Member]
Customer Securities for which Entity has Right to Sell or Repledge (Including Securities Sold or Repledged) [Line Items]
Total collateral available	31.4	23.8
Stock Borrowings [Member]
Customer Securities for which Entity has Right to Sell or Repledge (Including Securities Sold or Repledged) [Line Items]
Total collateral available	$ 0.8	$ 1.2

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Cash Deposited with and Securities Pledged to Clearinghouses (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Cash Deposited with and Securities Pledged to Clearinghouses [Line Items]
Cash deposited and securities pledged	$ 595	$ 549
Cash [Member] | Receivable from brokers, dealers and clearing organizations [Member]
Cash Deposited with and Securities Pledged to Clearinghouses [Line Items]
Cash deposited and securities pledged	545	151
U.S. government debt securities [Member] | Securities owned, at fair value [Member]
Cash Deposited with and Securities Pledged to Clearinghouses [Line Items]
Cash deposited and securities pledged	$ 50	$ 398

Commitments and Contingencies_4

Commitments and Contingencies - Additional Information (Detail)	9 Months Ended	12 Months Ended
	Jun. 30, 2018plaintiff	Sep. 30, 2018USD ($)litigation_caseplaintiffinvestor	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Aug. 09, 2018	Jul. 17, 2018USD ($)
Contingencies and Commitments [Line Items]
Rental expense, net of sublease income		$ 83,000,000	$ 54,000,000	$ 51,000,000
Contingent liability for guarantees to securities clearinghouses and exchanges		0	$ 0
Minimum [Member]
Contingencies and Commitments [Line Items]
Aggregate range of reasonably possible losses in excess of amounts accrued		0
Maximum [Member]
Contingencies and Commitments [Line Items]
Aggregate range of reasonably possible losses in excess of amounts accrued		$ 175,000,000
Order Routing Matters [Member]
Contingencies and Commitments [Line Items]
Claims previously filed | litigation_case		6
Claims dismissed | litigation_case		5
Pending claims | litigation_case		1
Lawsuit Regarding Scottrade Acquisition [Member]
Contingencies and Commitments [Line Items]
Maximum percentage of fees and expenses					20.00%
Aequitas Securities Litigation [Member]
Contingencies and Commitments [Line Items]
Alleged amount of securities purchased (more than $140 million)		$ 140,000,000
Alleged number of investors involved in the claim (more than 1,500) | investor		1,500
Alleged amount of securities owed to investors (more than $600 million)		$ 600,000,000
Number of plaintiffs | plaintiff		200
Alleged approximate losses plus other damages		$ 125,000,000
TD Ameritrade, Inc [Member] | Order Routing Matters [Member]
Contingencies and Commitments [Line Items]
Claims previously filed | litigation_case		5
Scottrade, Inc. [Member] | Order Routing Matters [Member]
Contingencies and Commitments [Line Items]
Claims previously filed | litigation_case		1
Non Class Action Lawsuits [Member] | Aequitas Securities Litigation [Member]
Contingencies and Commitments [Line Items]
Claims previously filed | plaintiff	5
Ciuffitelli Class Action [Member] | Aequitas Securities Litigation [Member]
Contingencies and Commitments [Line Items]
Preliminary settlement between plaintiffs and tonkon torp defendent						$ 18,500,000

Fair Value Disclosures - Fair V

Fair Value Disclosures - Fair Value Hierarchy for Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Assets
Securities owned	$ 156	$ 503
Investments available-for-sale, at fair value	484	746
Recurring [Member]
Assets
Investments segregated and on deposit for regulatory purposes	1,527	5,580
Securities owned	156	503
Other assets	4	28
Total assets at fair value	4,544	7,938
Recurring [Member] | U.S. Government Debt Securities [Member]
Assets
Investments segregated and on deposit for regulatory purposes	225	4,094
Securities owned	149	498
Investments available-for-sale, at fair value	484	746
Other assets	1	1
Recurring [Member] | U.S. Government Agency Mortgage-Backed Securities [Member]
Assets
Investments segregated and on deposit for regulatory purposes	1,302	1,486
Recurring [Member] | Other Securities [Member]
Assets
Securities owned	7	5
Recurring [Member] | Auction Rate Securities [Member]
Assets
Other assets	1	1
Recurring [Member] | Pay Variable Interest Rate Swap [Member]
Assets
Other assets	2	26
Liabilities
Accounts payable and other liabilities	96	3
Recurring [Member] | Money Market Funds [Member]
Assets
Cash equivalents	2,373	1,081
Level 1 [Member] | Recurring [Member]
Assets
Securities owned	1	1
Total assets at fair value	2,374	1,082
Level 1 [Member] | Recurring [Member] | Other Securities [Member]
Assets
Securities owned	1	1
Level 1 [Member] | Recurring [Member] | Money Market Funds [Member]
Assets
Cash equivalents	2,373	1,081
Level 2 [Member] | Recurring [Member]
Assets
Investments segregated and on deposit for regulatory purposes	1,527	5,580
Securities owned	155	502
Other assets	3	27
Total assets at fair value	2,169	6,855
Level 2 [Member] | Recurring [Member] | U.S. Government Debt Securities [Member]
Assets
Investments segregated and on deposit for regulatory purposes	225	4,094
Securities owned	149	498
Investments available-for-sale, at fair value	484	746
Other assets	1	1
Level 2 [Member] | Recurring [Member] | U.S. Government Agency Mortgage-Backed Securities [Member]
Assets
Investments segregated and on deposit for regulatory purposes	1,302	1,486
Level 2 [Member] | Recurring [Member] | Other Securities [Member]
Assets
Securities owned	6	4
Level 2 [Member] | Recurring [Member] | Pay Variable Interest Rate Swap [Member]
Assets
Other assets	2	26
Liabilities
Accounts payable and other liabilities	96	3
Level 3 [Member] | Recurring [Member]
Assets
Securities owned		0
Other assets	1	1
Total assets at fair value	1	1
Level 3 [Member] | Recurring [Member] | Auction Rate Securities [Member]
Assets
Other assets	$ 1	$ 1

Fair Value Disclosures - Additi

Fair Value Disclosures - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Reverse repurchase agreements, general maturity	7 days
Reverse repurchase agreements, included in other assets		$ 65
Debt Instrument [Line Items]
Long-term debt, aggregate carrying value	$ 2,439	2,555
Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt, aggregate estimated fair value	2,510	2,630
Long-term debt, aggregate carrying value	$ 2,440	$ 2,560

Offsetting Assets and Liabili_3

Offsetting Assets and Liabilities - Effect of Rights of Setoff Associated with Company's Recognized Assets and Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Offsetting Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed [Abstract]
Total recognized assets, gross	$ 1,305	$ 2,249
Total recognized assets, gross amounts offset in the balance sheet	0	0
Total recognized assets, net amounts presented in the balance sheet	1,305	2,249
Derivative Asset, Securities Purchased Under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Securities	(1,244)	(2,092)
Derivative Asset, Securities Purchased Under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Cash	(43)	(136)
Total recognized assets, net amount	18	21
Offsetting Securities Loaned [Abstract]
Deposits received for securities loaned, gross	2,914	2,449
Securities Sold under Agreements to Repurchase [Abstract]
Securities sold under agreements to repurchase, net amounts presented in the balance sheet	96	97
Securities pledged as collateral for repurchase agreements	(98)	(99)
Offsetting Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned [Abstract]
Total recognized liabilities, gross	3,106	2,549
Total recognized liabilities, gross amounts offset in the balance sheet	0	0
Total recognized liabilities, net amounts presented in the balance sheet	3,106	2,549
Derivative Liability, Securities Sold Under Agreements to Repurchase, Securities Loaned, Collateral, Right to Reclaim Securities	(2,544)	(2,113)
Derivative Liability, Securities Sold Under Agreements to Repurchase, Securities Loaned, Collateral, Right to Reclaim Cash	(221)	(210)
Total recognized liabilities, net amount	341	226
Investments segregated for regulatory purposes [Member]
Offsetting Securities Purchased under Agreements to Resell [Abstract]
Reverse repurchase agreements, gross	500	1,004
Reverse repurchase agreements, gross amounts offset in the balance sheet	0	0
Reverse repurchase agreements, net amounts presented in the balance sheet	500	1,004
Securities Purchased under Agreements to Resell, Collateral, Obligation to Return Securities	(500)	(1,004)
Securities Purchased under Agreements to Resell, Collateral, Obligation to Return Cash	0	0
Reverse repurchase agreements, net amount	0	0
Receivable from brokers, dealers and clearing organizations [Member]
Offsetting Securities Borrowed [Abstract]
Deposits paid for securities borrowed, gross	803	1,154
Deposits paid for securities borrowed, gross amounts offset in the balance sheet	0	0
Deposits paid for securities borrowed, net amounts presented in the balance sheet	803	1,154
Securities Borrowed, Collateral Obligation to Return Securities	(744)	(1,023)
Securities Borrowed, Collateral, Obligation to Return Cash	(41)	(110)
Deposits paid for securities borrowed, net amount	18	21
Other assets [Member]
Offsetting Securities Purchased under Agreements to Resell [Abstract]
Reverse repurchase agreements, gross		65
Reverse repurchase agreements, gross amounts offset in the balance sheet		0
Reverse repurchase agreements, net amounts presented in the balance sheet		65
Securities Purchased under Agreements to Resell, Collateral, Obligation to Return Securities		(65)
Securities Purchased under Agreements to Resell, Collateral, Obligation to Return Cash		0
Reverse repurchase agreements, net amount		0
Offsetting Derivative Assets [Abstract]
Pay-variable interest rate swaps, gross	2	26
Pay-variable interest rate swaps, gross amounts offset in the balance sheet	0	0
Pay-variable interest rate swaps, net amounts presented in the balance sheet	2	26
Derivative Collateral Obligation to Return Securities	0	0
Derivative Collateral Obligation to Return Cash	(2)	(26)
Pay-variable interest rate swaps, net amount	0	0
Offsetting Derivative Asset, Securities Purchased under Agreements to Resell, Securities Borrowed [Abstract]
Total recognized assets, gross		91
Total recognized assets, gross amounts offset in the balance sheet		0
Total recognized assets, net amounts presented in the balance sheet		91
Derivative Asset, Securities Purchased Under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Securities		(65)
Derivative Asset, Securities Purchased Under Agreements to Resell, Securities Borrowed, Collateral, Obligation to Return Cash		(26)
Total recognized assets, net amount		0
Payable to brokers, dealers and clearing organizations [Member]
Offsetting Securities Loaned [Abstract]
Deposits received for securities loaned, gross	2,914	2,449
Deposits received for securities loaned, gross amounts offset in the balance sheet	0	0
Deposits received for securities loaned, net amounts presented in the balance sheet	2,914	2,449
Securities Loaned Collateral Right To Reclaim Securities	(2,544)	(2,113)
Securities Loaned Collateral Right to Reclaim Cash	(43)	(112)
Deposits received for securities loaned, net amount	327	224
Securities sold under agreements to repurchase [Member]
Securities Sold under Agreements to Repurchase [Abstract]
Securities sold under agreements to repurchase, gross	96	97
Securities sold under agreements to repurchase, gross amount offset in the balance sheet	0	0
Securities sold under agreements to repurchase, net amounts presented in the balance sheet	96	97
Securities Sold Under Agreements to Repurchase, Collateral, Right to Reclaim Securities1	0	0
Securities pledged as collateral for repurchase agreements	(96)	(97)
Securities sold under agreements to repurchase, net amount	0	0
Accounts payable and other liabilities [Member]
Offsetting Derivative Liabilities [Abstract]
Pay-variable rate interest rate swaps, gross	96	3
Pay-variable rate interest rate swaps, gross amounts offset in the balance sheet	0	0
Pay-variable rate interest rate swaps, net amounts presented in the balance sheet	96	3
Derivative, Collateral, Right to Reclaim Securities	0	0
Derivative, Collateral, Right to Reclaim Cash	(82)	(1)
Pay-variable rate interest rate swaps, net amount	$ 14	$ 2

Offsetting Assets and Liabili_4

Offsetting Assets and Liabilities - Disaggregation of Secured Lending Transactions (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Gross Securities Lending Transactions [Line Items]
Deposits received for securities loaned, gross	$ 2,914	$ 2,449
Equity Securities [Member]
Disaggregation of Gross Securities Lending Transactions [Line Items]
Deposits received for securities loaned, gross	2,583	2,109
Exchange Traded Funds [Member]
Disaggregation of Gross Securities Lending Transactions [Line Items]
Deposits received for securities loaned, gross	223	230
Closed-end Funds [Member]
Disaggregation of Gross Securities Lending Transactions [Line Items]
Deposits received for securities loaned, gross	74	66
Other Securities [Member]
Disaggregation of Gross Securities Lending Transactions [Line Items]
Deposits received for securities loaned, gross	$ 34	$ 44

Offsetting Assets and Liabili_5

Offsetting Assets and Liabilities - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Offsetting Assets And Liabilities [Line Items]
Gross amounts of deposits paid for securities borrowed	$ 803	$ 1,154
Gross amounts of deposits received for securities loaned	2,914	2,449
Fair value of collateral the Company has received under enforceable master agreements	1,300	2,260
Fair value of collateral the Company has pledged under enforceable master agreements	2,760	2,320
Transacted Through the Option Clearing Corporation [Member]
Offsetting Assets And Liabilities [Line Items]
Gross amounts of deposits paid for securities borrowed	462	675
Gross amounts of deposits received for securities loaned	$ 2,010	$ 1,650

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss - Net Change (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Investments available-for-sale:
Unrealized loss	$ (12)	$ (9)	$ 0
Unrealized loss, tax effect	3	4	0
Unrealized loss, net of tax	(9)	(5)	0
Reclassification adjustment for realized losses included in net income, before tax	11	0	0
Reclassification adjustment for realized losses included in net income, tax effect	(4)	0	0
Reclassification adjustment for realized losses included in net income, net of tax	7	0	0
Net change in investments available-for-sale	(1)	(9)	0
Net change in investments available-for-sale, tax effect	(1)	4	0
Net change in investments available-for-sale, net of tax	(2)	(5)	0
Cash flow hedging instruments:
Reclassification adjustment for portion of realized loss amortized to net income	5	4	5
Reclassification adjustment for portion of realized loss amortized to net income, tax effect	(1)	(2)	(2)
Reclassification adjustment for portion of realized loss amortized to net income, net of tax	4	2	3
Net change in cash flow hedge instruments, before tax	5	4	5
Net change in cash flow hedging instruments, tax effect	(1)	(2)	(2)
Net change in cash flow hedging instruments, net of tax	4	2	3
Total other comprehensive income (loss), before tax	4	(5)	5
Income tax effect	(2)	2	(2)
Total other comprehensive income (loss), net of tax	$ 2	$ (3)	$ 3

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Loss - Balance Rollforward (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	$ 7,247	$ 5,051	$ 4,903
Ending balance, value	8,003	7,247	5,051
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	(25)	(22)	(25)
Current period change	(2)	(3)	3
Ending balance, value	(27)	(25)	(22)
Investments Available-for-sale [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	(5)	0	0
Other comprehensive loss before reclassification	(9)	(5)	0
Amount reclassified from accumulated other comprehensive loss	7	0	0
Current period change	(2)	(5)	0
Ending balance, value	(7)	(5)	0
Cash Flow Hedging Instruments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance, value	(20)	(22)	(25)
Amount reclassified from accumulated other comprehensive loss	4	2	3
Adoption of Accounting Standards Update 2018-02 (Note 1)	(4)	0	0
Current period change	0	2	3
Ending balance, value	$ (20)	$ (20)	$ (22)

Accelerated Stock Repurchase _2

Accelerated Stock Repurchase Agreements - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	Sep. 13, 2018	Sep. 12, 2018	Oct. 16, 2018	Jun. 30, 2016	Dec. 31, 2015	Jun. 08, 2016	Dec. 01, 2015
Accelerated Stock Repurchase Agreement - September 2018 [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Prepayment of accelerated stock repurchase agreement		$ 150
Initial delivery of shares repurchased under accelerated stock repurchase agreement	2.2
Accelerated stock repurchase program, percentage of shares	80.00%
Accelerated stock repurchase program, initial price paid per share		$ 54.69
Accelerated Stock Repurchase Agreement - June 2016 [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Prepayment of accelerated stock repurchase agreement						$ 42.5
Initial delivery of shares repurchased under accelerated stock repurchase agreement				1.1
Accelerated stock repurchase program, shares received upon settlement				0.3
Total shares repurchased under accelerated stock repurchase agreement				1.4
Accelerated stock repurchase program, final price paid per share				$ 29.89
Accelerated Stock Repurchase Agreement - December 2015 [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Prepayment of accelerated stock repurchase agreement							$ 45
Initial delivery of shares repurchased under accelerated stock repurchase agreement					1
Accelerated stock repurchase program, shares received upon settlement					0.3
Total shares repurchased under accelerated stock repurchase agreement					1.3
Accelerated stock repurchase program, final price paid per share					$ 33.98
Subsequent Event [Member] | Accelerated Stock Repurchase Agreement - September 2018 [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Accelerated stock repurchase program, shares received upon settlement			0.6
Total shares repurchased under accelerated stock repurchase agreement			2.8
Accelerated stock repurchase program, final price paid per share			$ 53.13

Related Party Transactions - Su

Related Party Transactions - Summary of Revenues Resulting from Transactions with Related Parties (Detail) - TD and its affiliates [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Related Party Transaction [Line Items]
Revenues from related parties	$ 1,456	$ 1,126	$ 944
Insured Deposit Account Agreement [Member] | Bank Deposit Account Fees [Member]
Related Party Transaction [Line Items]
Revenues from related parties	1,426	1,101	926
Mutual Fund Agreements [Member] | Investment Product Fees [Member]
Related Party Transaction [Line Items]
Revenues from related parties	17	15	11
Other [Member] | Various [Member]
Related Party Transaction [Line Items]
Revenues from related parties	$ 13	$ 10	$ 7

Related Party Transactions - _2

Related Party Transactions - Summary of Expenses Resulting from Transactions with Related Parties (Detail) - TD and its affiliates [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Related Party Transaction [Line Items]
Expenses to related parties	$ 7	$ 17	$ 26
Canadian Call Center Services Agreement [Member] | Various [Member]
Related Party Transaction [Line Items]
Expenses to related parties	0	11	22
Referral and Strategic Alliance Agreement [Member] | Other Expense [Member]
Related Party Transaction [Line Items]
Expenses to related parties	5	5	3
Other [Member] | Various [Member]
Related Party Transaction [Line Items]
Expenses to related parties	$ 2	$ 1	$ 1

Related Party Transactions - _3

Related Party Transactions - Summary of Classification and Amount of Receivables from and Payables to Affiliates of Company (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017
Assets:
Receivable from affiliates	$ 151	$ 137
Liabilities:
Payable to brokers, dealers and clearing organizations	2,980	2,504
Payable to affiliates	45	109
TD and its affiliates [Member]
Assets:
Receivable from affiliates	151	110
Liabilities:
Payable to brokers, dealers and clearing organizations	47	37
Payable to affiliates	$ 7	$ 38

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2018USD ($)board_of_directors_memberComponent	Sep. 30, 2017USD ($)
Related Party Transaction [Line Items]
Number of Board of Directors members, total | board_of_directors_member	12
Payable to subsidiaries and affiliates	$ 45,000,000	$ 109,000,000
Receivable from affiliates	$ 151,000,000	137,000,000
Insured Deposit Account Agreement [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Servicing fee percentage	0.25%
Insured Deposit Account Agreement [Member] | Minimum [Member]
Related Party Transaction [Line Items]
Servicing fee percentage	0.03%
TD and its affiliates [Member]
Related Party Transaction [Line Items]
Percentage ownership in the Company	42.00%
Number of Board of Directors members, designated by related party | board_of_directors_member	5
Payable to subsidiaries and affiliates	$ 7,000,000	38,000,000
Receivable from affiliates	$ 151,000,000	110,000,000
TD and its affiliates [Member] | Insured Deposit Account Agreement [Member]
Related Party Transaction [Line Items]
Related party transaction, agreement successive renewal term	5 years
Related party transaction, non-renewal terms, prior written notice period for termination of related party agreement by any party	2 years
Number of primary components related to the fee earned on IDA agreement | Component	2
Reset frequency of adjustments required to adjust variable rate leg of interest rate swaps under current IDA agreement	1 month
Percentage of fixed rate notional investments	78.00%
Percentage of floating rate investments	22.00%
Deposit amount threshold for floating-rate or fixed-rate notional investments with a maturity of up to 24 months subject to servicing fee adjustment	$ 20,000,000,000
Contingent liability carried on the Consolidated Balance Sheets	$ 0	0
TD and its affiliates [Member] | Insured Deposit Account Agreement [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Maturity of short-term fixed-rate notional investments	24 months
TD and its affiliates [Member] | Insured Deposit Account Agreement [Member] | New Fixed Rate Notional Investments [Member]
Related Party Transaction [Line Items]
Event one, federal funds effective rate, minimum	0.75%
Term of U.S. dollar interest rate swaps	5 years
Event two, minimum rate on five-year U.S. dollar interest rate swaps for 20 consecutive business days	1.50%
Event two, number of consecutive business days required above the minimum rate on U.S. dollar interest rate swaps for reduction in rate earned by Company	20 days
Percentage used in the calculation to reduce the rate earned by the Company on new fixed-rate notional investments in the case event one and event two are both fulfilled	20.00%
Maximum reduction to rate on new fixed-rate notional investments earned by Company in the case event one and event two are both fulfilled	0.10%
TD and its affiliates [Member] | Insured Deposit Account Agreement Fee Example [Member]
Related Party Transaction [Line Items]
Designated deposit amount	$ 100,000,000
Term of deposits invested in fixed rate investments	5 years
Term of applicable swaps	5 years
Fixed yield for applicable LIBOR-based swaps	1.45%
Gross fixed yield earned on deposits	1.45%
Management [Member]
Related Party Transaction [Line Items]
Payable to subsidiaries and affiliates	$ 38,000,000	71,000,000
Receivable from affiliates		$ 27,000,000

Condensed Financial Informati_3

Condensed Financial Information (Parent Company Only) - Schedule of Condensed Balance Sheets (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
ASSETS
Cash and cash equivalents	$ 2,690	$ 1,472	$ 1,855	$ 1,978
Receivable from subsidiaries	151	137
Investments available-for-sale, at fair value	484	746
Securities pledged as collateral for repurchase agreements	98	99
Total assets	37,520	38,627
Liabilities:
Accounts payable and other liabilities	896	815
Payable to affiliates	45	109
Securities sold under agreements to repurchase	96	97
Long-term debt	2,439	2,555
Total liabilities	29,517	31,380
Stockholders' equity	8,003	7,247	5,051	4,903
Total liabilities and stockholders' equity	37,520	38,627
TD Ameritrade Holding Corporation [Member]
ASSETS
Cash and cash equivalents	151	154	$ 248	$ 920
Receivable from subsidiaries	8	6
Investments available-for-sale, at fair value	484	746
Investments in subsidiaries	9,976	9,043
Other, net	162	108
Total assets	10,781	10,057
Liabilities:
Accounts payable and other liabilities	240	104
Payable to affiliates	3	54
Securities sold under agreements to repurchase	96	97
Long-term debt	2,439	2,555
Total liabilities	2,778	2,810
Stockholders' equity	8,003	7,247
Total liabilities and stockholders' equity	$ 10,781	$ 10,057

Condensed Financial Informati_4

Condensed Financial Information (Parent Company Only) - Schedule of Condensed Statements of Income (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Condensed Income Statements, Captions [Line Items]
Net revenues	$ 1,398	$ 1,382	$ 1,415	$ 1,257	$ 983	$ 931	$ 904	$ 859	$ 5,452	$ 3,676	$ 3,327
Operating expenses									3,454	2,210	2,009
Operating income	635	631	396	336	361	394	358	353	1,998	1,466	1,318
Other expense (income)									111	72	53
Pre-tax income									1,887	1,394	1,265
Provision for (benefit from) income taxes									414	522	423
Net income	$ 454	$ 451	$ 271	$ 297	$ 211	$ 231	$ 214	$ 216	1,473	872	842
TD Ameritrade Holding Corporation [Member]
Condensed Income Statements, Captions [Line Items]
Net revenues									52	31	30
Operating expenses									21	34	26
Operating income									31	(3)	4
Other expense (income)									106	71	53
Pre-tax income									(75)	(74)	(49)
Provision for (benefit from) income taxes									15	(22)	6
Income (loss) before equity in income of subsidiaries									(90)	(52)	(55)
Equity in income of subsidiaries									1,563	924	897
Net income									$ 1,473	$ 872	$ 842

Condensed Financial Informati_5

Condensed Financial Information (Parent Company Only) - Schedule of Condensed Statements of Cash Flows (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net income	$ 454	$ 451	$ 271	$ 297	$ 211	$ 231	$ 214	$ 216	$ 1,473	$ 872	$ 842
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income taxes									(24)	(11)	(8)
Loss on sale of investments									11	0	0
Stock-based compensation									60	36	34
Other, net									18	12	16
Changes in operating assets and liabilities:
Other assets									(39)	(5)	(17)
Accounts payable and other liabilities									(20)	31	(58)
Net cash provided by operating activities									1,908	699	1,484
Cash flows from investing activities:
Proceeds from sale of investments available-for-sale, at fair value									643	0	0
Purchase of investments available-for-sale, at fair value									(392)	0	(757)
Proceeds from sale and maturity of short-term investments									66	4	604
Purchase of short-term investments									(1)	(66)	(605)
Net cash provided by (used in) investing activities									92	(1,547)	(863)
Cash flows from financing activities:
Proceeds from issuance of long-term debt									0	798	0
Payment of debt issuance costs									(3)	(8)	0
Principal payments on long-term debt									0	(385)	0
Reimbursement (payment) of prepayment premium on long-term debt										(54)	0
Net Proceeds from (payments on) securities sold under agreements to repurchase									(1)	97	0
Proceeds from senior revolving credit facilities									3,225	0	0
Principal payments on senior revolving credit facilities									(3,225)	0	0
Payment of cash dividends									(477)	(379)	(362)
Proceeds from issuance of common stock									0	400	0
Purchase of treasury stock									(255)	0	(352)
Purchase of treasury stock for income tax withholding on stock-based compensation									(17)	(27)	(30)
Payment for future treasury stock under accelerated stock repurchase agreement									(31)	0	0
Net cash provided by (used in) financing activities									(782)	465	(744)
Net increase (decrease) in cash and cash equivalents									1,218	(383)	(123)
Cash and cash equivalents at beginning of year				1,472				1,855	1,472	1,855	1,978
Cash and cash equivalents at end of year	2,690				1,472				2,690	1,472	1,855
Supplemental cash flow information:
Interest paid									118	59	54
Income taxes paid									352	483	519
Noncash investing activities:
Issuance of common stock in acquisition									0	1,261	0
TD Ameritrade Holding Corporation [Member]
Cash flows from operating activities:
Net income									1,473	872	842
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in income of subsidiaries									(1,563)	(924)	(897)
Deferred income taxes									13	(12)	0
Dividends from subsidiaries									1,030	1,230	825
Loss on sale of investments									11	0	0
Stock-based compensation									60	36	34
Other, net									9	9	8
Changes in operating assets and liabilities:
Receivable from subsidiaries									(2)	2	(3)
Other assets									(92)	0	1
Accounts payable and other liabilities									42	(67)	38
Payable to subsidiaries and affiliates									(24)	(4)	26
Net cash provided by operating activities									957	1,142	874
Cash flows from investing activities:
Investment in subsidiaries									(425)	(15)	(60)
Loans made under intercompany credit agreements									(175)	0	0
Collections on intercompany credit agreements									175	0	0
Cash paid in business acquisition									(4)	(1,698)	0
Proceeds from sale of investments available-for-sale, at fair value									643	0	0
Purchase of investments available-for-sale, at fair value									(392)	0	(757)
Proceeds from sale and maturity of short-term investments									0	0	600
Purchase of short-term investments									0	0	(601)
Net cash provided by (used in) investing activities									(178)	(1,713)	(818)
Cash flows from financing activities:
Proceeds from issuance of long-term debt									0	798	0
Payment of debt issuance costs									(3)	(8)	0
Principal payments on long-term debt									0	(385)	0
Reimbursement (payment) of prepayment premium on long-term debt									2	(54)	0
Net Proceeds from (payments on) securities sold under agreements to repurchase									(1)	97	0
Proceeds from senior revolving credit facilities									200	0	0
Principal payments on senior revolving credit facilities									(200)	0	0
Payment of cash dividends									(477)	(379)	(362)
Proceeds from issuance of common stock									0	400	0
Purchase of treasury stock									(255)	0	(352)
Purchase of treasury stock for income tax withholding on stock-based compensation									(17)	(27)	(30)
Payment for future treasury stock under accelerated stock repurchase agreement									(31)	0	0
Other, net									0	35	16
Net cash provided by (used in) financing activities									(782)	477	(728)
Net increase (decrease) in cash and cash equivalents									(3)	(94)	(672)
Cash and cash equivalents at beginning of year				$ 154				$ 248	154	248	920
Cash and cash equivalents at end of year	$ 151				$ 154				151	154	248
Supplemental cash flow information:
Interest paid									94	50	47
Income taxes paid									309	452	488
Noncash investing activities:
Issuance of common stock in acquisition									0	1,261	0
Assets transferred to a subsidiary, net									$ 0	$ 15	$ 0

Quarterly Data - Schedule of Qu

Quarterly Data - Schedule of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Quarterly Financial Information Disclosure [Abstract]
Net revenues	$ 1,398	$ 1,382	$ 1,415	$ 1,257	$ 983	$ 931	$ 904	$ 859	$ 5,452	$ 3,676	$ 3,327
Operating income	635	631	396	336	361	394	358	353	1,998	1,466	1,318
Net income	$ 454	$ 451	$ 271	$ 297	$ 211	$ 231	$ 214	$ 216	$ 1,473	$ 872	$ 842
Basic earnings per share (in usd per share)	$ 0.80	$ 0.79	$ 0.48	$ 0.52	$ 0.40	$ 0.44	$ 0.41	$ 0.41	$ 2.60	$ 1.65	$ 1.59
Diluted earnings per share (in usd per share)	$ 0.80	$ 0.79	$ 0.48	$ 0.52	$ 0.39	$ 0.44	$ 0.40	$ 0.41	$ 2.59	$ 1.64	$ 1.58

Subsequent Event - Additional I

Subsequent Event - Additional Information (Details) - USD ($) $ in Millions	Oct. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Subsequent Event [Line Items]
Debt instrument, face value		$ 2,646	$ 2,647
Senior Notes [Member]
Subsequent Event [Line Items]
Debt instrument, face value		$ 2,550	$ 2,550
Senior Notes [Member] | 2021 Notes [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, face value	$ 600
Senior Notes [Member] | 2024 Notes [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, face value	$ 400
Interest rate, stated percentage	3.75%
Senior Notes [Member] | Senior Notes Due 2021 And 2024 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, face value	$ 1,000
Debt instrument, redemption price, percentage	100.00%
LIBOR [Member] | Senior Notes [Member] | 2021 Notes [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, basis spread on variable rate	0.43%
US Treasury Rate [Member] | Senior Notes [Member] | Senior Notes Due 2021 And 2024 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, basis spread on variable rate	0.15%