Commitments and Contingencies (Details) account in Millions			3 Months Ended
	Nov. 20, 2019 USD ($)	Jul. 25, 2019 USD ($) account	Mar. 31, 2020 USD ($)	Nov. 25, 2019 USD ($) account shares
Loss Contingencies [Line Items]
Aggregate face amount of letter of credit agreements			$ 20,000,000
Number of brokerage and managed portfolio accounts acquired | account		1,000,000
Client assets acquired		$ 90,000,000,000
Payments to acquire businesses		$ 1,800,000,000
TD Ameritrade [Member]
Loss Contingencies [Line Items]
Number of brokerage and managed portfolio accounts acquired | account				12,000,000
Client assets acquired				$ 1,300,000,000,000
Conversion of shares (in shares) | shares				1.0837
Merger consideration	$ 26,000,000,000
Termination fee			950,000,000
Reimbursement fee			50,000,000
Performance Guarantee [Member]
Loss Contingencies [Line Items]
Liability for guarantees			0
U.S. Treasury securities [Member]
Loss Contingencies [Line Items]
U.S. Treasury securities posted as collateral			212,000,000
Margin Requirements [Member]
Loss Contingencies [Line Items]
Funds drawn under LOC's			$ 0