Regulatory Capital Requirements - Summary of Regulatory Capital Requirements (Details) $ in Thousands	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Tier 1 leverage ratio
Capital conservation buffer	2.50%	2.50%
TCF
Regulatory Capital:
Common equity Tier 1 capital	$ 4,101,896	$ 4,103,007
Tier 1 capital	4,299,135	4,290,793
Total capital	$ 4,994,676	$ 5,026,611
Common equity Tier 1 capital ratio
Common equity Tier 1 capital - actual, ratio	0.1106	0.1145
Risk-based capital ratios
Tier 1 risk-based capital - actual, ratio	0.1159	0.1198
Total risk-based capital - actual, ratio	0.1347	0.1403
Tier 1 leverage ratio
Tier 1 leverage - actual, ratio	0.0909	0.0934
TCF Bank
Regulatory Capital:
Common equity Tier 1 capital	$ 4,095,564	$ 4,093,974
Tier 1 capital	4,123,501	4,112,458
Total capital	$ 4,799,935	$ 4,831,026
Common equity Tier 1 capital ratio
Common equity Tier 1 capital - actual, ratio	0.1106	0.1145
Common equity Tier 1 capital - well-capitalized capital requirement, ratio	6.50%
Common equity Tier 1 capital - minimum capital requirement, ratio	4.50%
Risk-based capital ratios
Tier 1 risk-based capital - actual, ratio	0.1114	0.1150
Tier 1 risk-based capital - well-capitalized capital requirement, ratio	0.0800
Tier 1 risk-based capital - minimum capital requirement, ratio	0.0600
Total risk-based capital - actual, ratio	0.1296	0.1351
Total risk-based capital - well-capitalized capital requirement, ratio	0.1000
Total risk-based capital - minimum capital requirement, ratio	0.0800
Tier 1 leverage ratio
Tier 1 leverage - actual, ratio	0.0873	0.0897
Tier 1 leverage - well-capitalized capital requirement, ratio	0.0500
Tier 1 leverage - minimum capital requirement, ratio	0.0400