Regulatory Capital Requirements - Summary of Regulatory Capital Requirements (Details) $ in Thousands	Sep. 30, 2020 USD ($)	Jan. 01, 2020 USD ($)	Dec. 31, 2019 USD ($)
Tier 1 leverage ratio
Capital conservation buffer	2.50%		2.50%
TCF
Regulatory Capital:
Common equity Tier 1 capital	$ 4,053,931		$ 4,050,826
Tier 1 capital	4,244,609		4,236,648
Total capital	$ 4,972,715	$ (159,300)	$ 4,681,630
Common equity Tier 1 capital ratio
Common equity Tier 1 capital - actual, ratio	0.1145		0.1099
Risk-based capital ratios
Tier 1 risk-based capital - actual, ratio	0.1198		0.1149
Total risk-based capital - actual, ratio	0.1404		0.1270
Tier 1 leverage ratio
Tier 1 leverage - actual, ratio	0.0883		0.0949
TCF Bank
Regulatory Capital:
Common equity Tier 1 capital	$ 4,029,278		$ 4,039,191
Tier 1 capital	4,050,654		4,059,417
Total capital	$ 4,769,055		$ 4,524,051
Common equity Tier 1 capital ratio
Common equity Tier 1 capital - actual, ratio	0.1139		0.1097
Common equity Tier 1 capital - well-capitalized capital requirement, ratio	6.50%
Common equity Tier 1 capital - minimum capital requirement, ratio	7.00%
Risk-based capital ratios
Tier 1 risk-based capital - actual, ratio	0.1145		0.1103
Tier 1 risk-based capital - well-capitalized capital requirement, ratio	0.0800
Tier 1 risk-based capital - minimum capital requirement, ratio	0.0850
Total risk-based capital - actual, ratio	0.1348		0.1229
Total risk-based capital - well-capitalized capital requirement, ratio	0.1000
Total risk-based capital - minimum capital requirement, ratio	0.1050
Tier 1 leverage ratio
Tier 1 leverage - actual, ratio	0.0843		0.0910
Tier 1 leverage - well-capitalized capital requirement, ratio	0.0500
Tier 1 leverage - minimum capital requirement, ratio	0.0400