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Condensed Financial Information of the Parent Company - Condensed Statements of Income (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Condensed Financial Statements, Captions [Line Items] |  |  |  |
Other income | [1] | $ 35 | $ 31 | $ 120
Total interest income |  | 7,927 | 5,412 | 4,367
Interest on long-term debt with subsidiary trusts |  | 1,305 | 475 | 221
Income (loss) from continuing operations before income taxes (TE) |  | 1,190 | 2,360 | 3,281
Income tax (expense) benefit |  | (196) | (422) | (642)
NET INCOME (LOSS) |  | 967 | 1,917 | 2,625
Less: Net income attributable to noncontrolling interests |  | 0 | 0 | 0
NET INCOME (LOSS) ATTRIBUTABLE TO KEY |  | 967 | 1,917 | 2,625
Key |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |
Interest income from subsidiaries |  | 15 | 4 | 1
Other income |  | 24 | 7 | 36
Total interest income |  | 714 | 586 | 2,012
Interest on long-term debt with subsidiary trusts |  | 33 | 19 | 13
Interest on other borrowed funds |  | 273 | 130 | 65
Personnel and other expense |  | 111 | 101 | 101
Total expense |  | 417 | 250 | 179
Income (loss) from continuing operations before income taxes (TE) |  | 297 | 336 | 1,833
Income tax (expense) benefit |  | 95 | 60 | 38
Income (loss) before equity in net income (loss) less dividends from subsidiaries |  | 392 | 396 | 1,871
Equity in net income (loss) less dividends from subsidiaries |  | 575 | 1,521 | 754
NET INCOME (LOSS) |  | 967 | 1,917 | 2,625
Less: Net income attributable to noncontrolling interests |  | 0 | 0 | 0
NET INCOME (LOSS) ATTRIBUTABLE TO KEY |  | 967 | 1,917 | 2,625
Key | Banks |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |
Dividends from subsidiaries: |  | 675 | 475 | 1,925
Key | Nonbank subsidiaries |  |  |  |
Condensed Financial Statements, Captions [Line Items] |  |  |  |
Dividends from subsidiaries: |  | $ 0 | $ 100 | $ 50
[1] | Net securities gains (losses) totaled $(11) million for the year ended December 31, 2023, $9 million for the year ended December 31, 2022, and $7 million for the year ended December 31, 2021.

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