Regulatory Capital (Tier 1 Capital And Total Capital Components) (Parenthetical) (Details)	Mar. 31, 2020
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 Capital ratio, minimum stated	4.50%
Tier 1 capital ratio, minimum stated	6.00%
Total capital ratio, minimum stated	8.00%
Capital conservation buffer rate	2.50%
CIT Bank, N.A.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Capital conservation buffer rate	2.50%