Borrowings (Long-term Debt Including Unamortized Debt Discounts and Premiums) (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Other financing	$ 108	$ 6
Unamortized premium — net	211	249
Debt issuance costs	(92)	(54)
Long-term Debt	18,708	13,632
Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes	14,931	9,881
Senior Notes [Member] \| TD Ameritrade [Member]
Debt Instrument [Line Items]
Senior Notes	$ 3,550	3,550
Senior Notes [Member] \| Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.25%
Senior Notes	$ 0	600
Senior Notes [Member] \| Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.225%
Senior Notes	$ 256	256
Senior Notes [Member] \| Senior Notes Due 2022 [Member] \| TD Ameritrade [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	2.95%
Senior Notes	$ 750	750
Senior Notes [Member] \| Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	2.65%
Senior Notes	$ 800	800
Senior Notes [Member] \| Senior Notes Due February 2024 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.55%
Senior Notes	$ 500	500
Senior Notes [Member] \| Senior Notes Due March 2024 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	0.75%
Senior Notes	$ 1,500	0
Senior Notes [Member] \| Senior Notes Due 2024 [Member] \| TD Ameritrade [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.75%
Senior Notes	$ 400	400
Senior Notes [Member] \| Senior Notes Due March 10, 2025 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.00%
Senior Notes	$ 375	375
Senior Notes [Member] \| Senior Notes Due March 2025 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	4.20%
Senior Notes	$ 600	600
Senior Notes [Member] \| Senior Notes Due May 2025 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.85%
Senior Notes	$ 750	750
Senior Notes [Member] \| Senior Notes Due 2025 [Member] \| TD Ameritrade [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.625%
Senior Notes	$ 500	500
Senior Notes [Member] \| Senior Notes Due February 2026 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.45%
Senior Notes	$ 350	350
Senior Notes [Member] \| Senior Notes Due March 2026 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	0.90%
Senior Notes	$ 1,250	1,250
Senior Notes [Member] \| Senior Notes Due May 2026 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	1.15%
Senior Notes	$ 1,000	0
Senior Notes [Member] \| Senior Notes Due 2027 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.20%
Senior Notes	$ 650	650
Senior Notes [Member] \| Senior Notes Due 2027 [Member] \| TD Ameritrade [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.30%
Senior Notes	$ 800	800
Senior Notes [Member] \| Senior Notes Due January 2028 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.20%
Senior Notes	$ 700	700
Senior Notes [Member] \| Senior Notes Due March 2028 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	2.00%
Senior Notes	$ 1,250	0
Senior Notes [Member] \| Senior Notes Due February 2029 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	4.00%
Senior Notes	$ 600	600
Senior Notes [Member] \| Senior Notes Due May 2029 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	3.25%
Senior Notes	$ 600	600
Senior Notes [Member] \| Senior Notes Due 2029 [Member] \| TD Ameritrade [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	2.75%
Senior Notes	$ 500	500
Senior Notes [Member] \| Senior Notes Due 2030 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	4.625%
Senior Notes	$ 500	500
Senior Notes [Member] \| Senior Notes Due March 2031 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	1.65%
Senior Notes	$ 750	750
Senior Notes [Member] \| Senior Notes Due May 2031 [Member]
Debt Instrument [Line Items]
Fixed Interest Rate	2.30%
Senior Notes	$ 750	0
Senior Notes [Member] \| Floating Rate Senior Notes Due 2021 [Member]
Debt Instrument [Line Items]
Senior Notes	$ 0	600
Senior Notes [Member] \| Floating Rate Senior Notes Due 2021 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Basis spread rate	0.32%
Senior Notes [Member] \| Floating Rate Senior Notes Due 2021 [Member] \| LIBOR [Member] \| TD Ameritrade [Member]
Debt Instrument [Line Items]
Basis spread rate	0.43%
Senior Notes [Member] \| Floating Rate Senior Notes Due 2024 [Member]
Debt Instrument [Line Items]
Senior Notes	$ 1,250	0
Senior Notes [Member] \| Floating Rate Senior Notes Due 2024 [Member] \| SOFR [Member]
Debt Instrument [Line Items]
Basis spread rate	0.50%
Senior Notes [Member] \| Floating Rate Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Senior Notes	$ 500	0
Senior Notes [Member] \| Floating Rate Senior Notes Due 2026 [Member] \| SOFR [Member]
Debt Instrument [Line Items]
Basis spread rate	0.52%
Senior Notes [Member] \| Various Rates Debt Due 2021 [Member] \| TD Ameritrade [Member]
Debt Instrument [Line Items]
Senior Notes	$ 600	$ 600

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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No definition available.

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- Definition

Amount, after accumulated amortization, of debt premium.

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- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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