Shareholders' Equity - Key's and KeyBank's Actual Capital Amounts and Ratios, Minimum Capital Amounts and Ratios (Details) $ in Millions	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Key
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital to net risk-weighted assets, actual amount	$ 21,028	$ 20,776
Tier 1 capital to net risk-weighted assets, actual amount	17,340	17,225
Tier 1 capital to average quarterly tangible assets, amount	$ 17,340	$ 17,225
Total capital to net risk-weighted assets, actual ratio	0.1415	0.1279
Tier 1 capital to net risk-weighted assets, actual ratio	0.1167	0.1060
Tier 1 capital to average quarterly tangible assets, actual ratio	0.0903	0.0888
Total capital to net risk-weighted assets, to meet minimum capital adequacy requirements, amount	$ 11,886	$ 12,998
Tier 1 capital to net risk-weighted assets, to meet minimum capital adequacy requirements, amount	8,914	9,748
Tier 1 capital to average quarterly tangible assets to meet minimum capital adequacy requirements, amount	$ 7,678	$ 7,759
Total capital to net risk-weighted assets, to meet minimum capital adequacy requirements, ratio	0.0800	0.0800
Tier 1 capital to net risk-weighted assets, to meet minimum capital adequacy requirements, ratio	0.0600	0.0600
Tier 1 capital to average quarterly tangible assets to meet minimum capital adequacy requirements, ratio	0.0400	0.0400
KeyBank (consolidated)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total capital to net risk-weighted assets, actual amount	$ 20,726	$ 19,903
Tier 1 capital to net risk-weighted assets, actual amount	17,487	16,801
Tier 1 capital to average quarterly tangible assets, amount	$ 17,487	$ 16,801
Total capital to net risk-weighted assets, actual ratio	0.1416	0.1239
Tier 1 capital to net risk-weighted assets, actual ratio	0.1194	0.1046
Tier 1 capital to average quarterly tangible assets, actual ratio	0.0922	0.0878
Total capital to net risk-weighted assets, to meet minimum capital adequacy requirements, amount	$ 11,712	$ 12,850
Tier 1 capital to net risk-weighted assets, to meet minimum capital adequacy requirements, amount	8,784	9,638
Tier 1 capital to average quarterly tangible assets to meet minimum capital adequacy requirements, amount	$ 7,587	$ 7,657
Total capital to net risk-weighted assets, to meet minimum capital adequacy requirements, ratio	0.0800	0.0800
Tier 1 capital to net risk-weighted assets, to meet minimum capital adequacy requirements, ratio	0.0600	0.0600
Tier 1 capital to average quarterly tangible assets to meet minimum capital adequacy requirements, ratio	0.0400	0.0400
Total capital to net risk-weighted assets, to qualify as well capitalized under federal deposit insurance act, amount	$ 14,640	$ 16,063
Tier 1 capital to net risk-weighted assets, to qualify as well capitalized under federal deposit insurance act, amount	11,712	12,850
Tier 1 capital to average quarterly tangible assets to qualify as well capitalized under federal deposit insurance act, amount	$ 9,483	$ 9,572
Total capital to net risk-weighted assets, to qualify as well capitalized under federal deposit insurance act, ratio	0.1000	0.1000
Tier 1 capital to net risk-weighted assets, to qualify as well capitalized under federal deposit insurance act, ratio	0.0800	0.0800
Tier 1 capital to average quarterly tangible assets to qualify as well capitalized under federal deposit insurance act, ratio	5.00%	5.00%

Tangible Capital Qualify As Well Capitalized Under Federal Deposit Insurance Act

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