Shareholders' Equity - Key's and KeyBank's Actual Capital Amounts and Ratios, Minimum Capital Amounts and Ratios (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Key [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Net Risk-Weighted Assets, Actual Amount	$ 16,731	$ 15,953
Tier 1 Capital to Average Quarterly Tangible Assets, Amount	14,207	13,712
Tier 1 Capital to Net Risk-Weighted Assets, Actual Amount	$ 14,207	$ 13,712
Total Capital to Net Risk-Weighted Assets, Actual Ratio	12.79%	12.89%
Tier 1 Capital to Net Risk-Weighted Assets, Actual Ratio	10.86%	11.08%
Tier 1 Capital to Average Quarterly Tangible Assets, Actual Ratio	9.87%	9.89%
Total Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Amount	$ 10,469	$ 9,903
Tier 1 Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Amount	7,852	7,427
Tier 1 Capital to Average Quarterly Tangible Assets to Meet Minimum Capital Adequacy Requirements, Amount	$ 5,756	$ 5,548
Total Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Ratio	8.00%	8.00%
Tier 1 Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Ratio	6.00%	6.00%
Tier 1 Capital to Average Quarterly Tangible Assets to Meet Minimum Capital Adequacy Requirements, Ratio	4.00%	4.00%
KeyBank (consolidated) [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Capital to Net Risk-Weighted Assets, Actual Amount	$ 16,313	$ 15,432
Tier 1 Capital to Average Quarterly Tangible Assets, Amount	14,091	13,575
Tier 1 Capital to Net Risk-Weighted Assets, Actual Amount	$ 14,091	$ 13,575
Total Capital to Net Risk-Weighted Assets, Actual Ratio	12.69%	12.68%
Tier 1 Capital to Net Risk-Weighted Assets, Actual Ratio	10.96%	11.16%
Tier 1 Capital to Average Quarterly Tangible Assets, Actual Ratio	9.91%	9.93%
Total Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Amount	$ 10,287	$ 9,733
Tier 1 Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Amount	7,715	7,300
Tier 1 Capital to Average Quarterly Tangible Assets to Meet Minimum Capital Adequacy Requirements, Amount	$ 5,688	$ 5,470
Total Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Ratio	8.00%	8.00%
Tier 1 Capital to Net Risk-Weighted Assets, to Meet Minimum Capital Adequacy Requirements, Ratio	6.00%	6.00%
Tier 1 Capital to Average Quarterly Tangible Assets to Meet Minimum Capital Adequacy Requirements, Ratio	4.00%	4.00%
Total Capital to Net Risk-Weighted Assets, to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Amount	$ 12,858	$ 12,166
Tier 1 Capital to Net Risk-Weighted Assets, to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Amount	7,715	7,300
Tier 1 Capital to Average Quarterly Tangible Assets to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Amount	$ 7,110	$ 6,838
Total Capital to Net Risk-Weighted Assets, to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Ratio	10.00%	10.00%
Tier 1 Capital to Net Risk-Weighted Assets, to Qualify as Well Capitalized Under Federal Deposit Insurance Act, Ratio	6.00%	6.00%
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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The amount of total capital as defined in the regulations.

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The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The minimum Total risk based capital ratio (total capital divided by risk weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Tangible capital as defined in the regulations (generally includes outstanding stock plus retained earnings) for banking institutions subject to Office of Thrift Supervision (OTS) capital requirements.

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The minimum amount of tangible capital required under the regulatory framework for prompt corrective action.

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The minimum amount of Tangible Capital divided by tangible assets (Tangible Capital Ratio) as defined in the regulations.

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Tangible Capital divided by Tangible assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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