Borrowings - Schedule of Short-term Borrowings (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Amount	$ 3,482,535	$ 2,669,145
Weighted-average Rate	0.66%	1.75%
FHLB advances
Short-term Debt [Line Items]
Amount	$ 3,200,000	$ 2,450,000
Weighted-average Rate	0.61%	1.85%
Collateralized Deposits
Short-term Debt [Line Items]
Amount	$ 202,535	$ 219,145
Weighted-average Rate	0.64%	0.64%
TCF Financial Corporation, Line-of-Credit | Line of Credit
Short-term Debt [Line Items]
Amount	$ 80,000	$ 0
Weighted-average Rate	2.64%	0.00%