Regulatory Requirements and Subsidiary Dividend Restrictions - Customer Reserve Requirements (Details) - USD ($) $ in Millions	Oct. 02, 2020	Sep. 30, 2020
Customer Reserve Requirement [Member]
Capital and Other Regulatory Requirements [Line Items]
Cash reserve deposit required		$ 18.5
Customer SRBA [Member]
Capital and Other Regulatory Requirements [Line Items]
Cash reserve deposit required		17.3
Customer SRBA [Member] | Subsequent Event [Member]
Capital and Other Regulatory Requirements [Line Items]
Cash reserve deposit required and made	$ 6.2
PAB Reserve Requirement [Member]
Capital and Other Regulatory Requirements [Line Items]
Cash reserve deposit required		2.2
PAB SRBA [Member]
Capital and Other Regulatory Requirements [Line Items]
Cash reserve deposit required		$ 2.1
PAB SRBA [Member] | Subsequent Event [Member]
Capital and Other Regulatory Requirements [Line Items]
Cash reserve deposit required and made	$ 1.1