Commitments and Contingencies (Details) account in Millions		6 Months Ended
	Nov. 20, 2019 USD ($)	Jun. 30, 2020 USD ($) lawsuit	May 12, 2020	Nov. 25, 2019 USD ($) account shares
Loss Contingencies [Line Items]
Aggregate face amount of letter of credit agreements		$ 20,000,000
Number of lawsuits filed | lawsuit		8
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
Business Acquisition, Percentage of Voting In Favor Of Acquisition			76.90%
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		242,000,000
Margin Requirements [Member]
Loss Contingencies [Line Items]
Funds drawn under LOC's		$ 0