Borrowings (Narrative) (Details)	6 Months Ended
Jun. 30, 2021 USD ($) loan_facility	Dec. 31, 2020 USD ($)
Line of Credit Facility [Line Items]
Maturity term	270 days
Commercial paper outstanding	$ 1,500,000,000	$ 0
Federal Reserve Bank stock	310,000,000	191,000,000
TD Ameritrade Clearing, Inc [Member]
Line of Credit Facility [Line Items]
Borrowings outstanding	2,000,000,000.0	0
Unsecured Debt [Member] \| TD Ameritrade Clearing, Inc [Member]
Line of Credit Facility [Line Items]
Amounts outstanding	0	0
Total borrowing capacity	$ 600,000,000
Number of credit facilities \| loan_facility	1
Unsecured Debt [Member] \| TD Ameritrade Clearing, Inc [Member] \| Debt Due 2021 [Member]
Line of Credit Facility [Line Items]
Total borrowing capacity		850,000,000
Federal Home Loan Bank Advances [Member]
Line of Credit Facility [Line Items]
Amounts outstanding	$ 0	0
FHLB stock	29,000,000	29,000,000
Total borrowing capacity	9,500,000,000	7,900,000,000
Federal Home Loan Bank Advances [Member] \| Secured Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	55,000,000,000.0	55,100,000,000
Amounts outstanding	$ 0	$ 0

Debt Instrument, Number Of Credit Facilities

No definition available.

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- Definition

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

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- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 325
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- Definition

Federal Reserve Bank stock represents an equity interest in the Federal Reserve Bank. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 1
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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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