Regulatory Matters (Details) $ in Thousands	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Associated Banc-Corp
Regulatory Capital [Abstract]
Total capital	$ 3,632,807	$ 3,208,625
Total Capital Actual Ratio	0.1402	0.1321
Total Capital for Capital Adequacy Purposes Amount	$ 2,072,273	$ 1,943,711
Total Capital for Adequacy Purposes Ratio	0.0800	0.0800
Tier 1 Capital Actual Amount	$ 3,058,809	$ 2,736,776
Tier 1 Capital Actual Ratio	0.1181	0.1126
Tier 1 Capital for Adequacy Purposes Amount	$ 1,554,205	$ 1,457,783
Tier 1 Capital for Adequacy Purposes Ratio	0.0600	0.0600
Common Equity Tier One Capital	$ 2,706,010	$ 2,480,698
Common Equity Tier One Capital to Risk Weighted Assets	10.45%	10.21%
Common Equity Tier One Capital Required for Capital Adequacy	$ 1,165,654	$ 1,093,337
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Tier 1 Leverage Capital Actual Amount	$ 3,058,809	$ 2,736,776
Tier 1 Leverage Capital Actual Ratio	0.0937	0.0883
Tier 1 Leverage Capital for Adequacy Purposes Amount	$ 1,305,604	$ 1,239,431
Tier 1 Leverage Capital for Adequacy Purposes Ratio	0.0400	0.0400
Associated Bank, N.A.
Regulatory Capital [Abstract]
Total capital	$ 3,295,823	$ 2,892,650
Total Capital Actual Ratio	0.1274	0.1195
Total Capital for Capital Adequacy Purposes Amount	$ 2,068,801	$ 1,936,732
Total Capital for Adequacy Purposes Ratio	0.0800	0.0800
Total Capital to be Well Capitalized Amount	$ 2,586,002	$ 2,420,915
Total Capital to be Well Capitalized Ratio	0.1000	0.1000
Tier 1 Capital Actual Amount	$ 2,971,234	$ 2,669,372
Tier 1 Capital Actual Ratio	0.1149	0.1103
Tier 1 Capital for Adequacy Purposes Amount	$ 1,551,601	$ 1,452,549
Tier 1 Capital for Adequacy Purposes Ratio	0.0600	0.0600
Tier 1 Capital To Be Well Capitalized Amount	$ 2,068,801	$ 1,936,732
Tier 1 Capital To Be Well Capitalized Ratio	0.0800	0.0800
Common Equity Tier One Capital	$ 2,971,234	$ 2,469,578
Common Equity Tier One Capital to Risk Weighted Assets	11.49%	10.20%
Common Equity Tier One Capital Required for Capital Adequacy	$ 1,163,701	$ 1,089,412
Common Equity Tier One Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.50%
Tier 1 Equity Capital to be Well Capitalized Amount	$ 1,680,901	$ 1,573,595
Tier 1 Equity Capital to be Well Capitalized Ratio	6.50%	6.50%
Tier 1 Leverage Capital Actual Amount	$ 2,971,234	$ 2,669,372
Tier 1 Leverage Capital Actual Ratio	0.0911	0.0863
Tier 1 Leverage Capital for Adequacy Purposes Amount	$ 1,304,448	$ 1,236,565
Tier 1 Leverage Capital for Adequacy Purposes Ratio	0.0400	0.0400
Tier 1 Leverage Capital To Be Well Capitalized Amount	$ 1,630,560	$ 1,545,706
Tier 1 Leverage Capital To Be Well Capitalized Ratio	0.0500	0.0500