Borrowings - Schedule of Short-term Borrowings (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Amount	$ 655,461	$ 2,669,145
Weighted-average Rate	0.28%	1.75%
FHLB advances
Short-term Debt [Line Items]
Amount	$ 400,000	$ 2,450,000
Weighted-average Rate	0.37%	1.85%
Collateralized Deposits
Short-term Debt [Line Items]
Amount	$ 253,959	$ 219,145
Weighted-average Rate	0.14%	0.64%
Line-of-Credit - TCF Financial Corporation | Line of Credit
Short-term Debt [Line Items]
Amount	$ 1,502	$ 0
Weighted-average Rate	1.50%	0.00%