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	Dec. 31, 2019	Sep. 30, 2019
Derivative [Line Items]
Pledged collateral from interest rate swap counterparty, aggregate fair value	$ 47	$ 86
Pledged collateral to interest rate swap counterparty, aggregate fair value	$ 16	$ 3

The aggregate fair value of assets pledged from the counterparty, at the end of the reporting period, as collateral for outstanding interest rate swap derivative instruments.

No definition available.

Name:	amtd_PledgedCollateralFromInterestRateSwapCounterpartyAggregateFairValue
Namespace Prefix:	amtd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant