Regulatory Requirements (Net Capital and Net Capital Requirements for CS&Co) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Net capital	$ 3,602,000	$ 3,117,000
Minimum dollar requirement	1,000	1,000
2% of aggregate debit balances	832,000	616,000
Net capital in excess of required net capital	2,770,000	2,501,000
TD Ameritrade Clearing, Inc [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Net capital	5,239,000	4,040,000
Minimum dollar requirement	1,500	1,500
2% of aggregate debit balances	971,000	748,000
Net capital in excess of required net capital	4,268,000	3,292,000
TD Ameritrade [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Net capital	624,000	350,000
Minimum dollar requirement	250	250
2% of aggregate debit balances	0	0
Net capital in excess of required net capital	$ 624,000	$ 350,000