Shareholders' Equity - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	0 Months Ended	1 Months Ended	3 Months Ended		12 Months Ended			12 Months Ended		3 Months Ended	12 Months Ended
	Nov. 14, 2008	Apr. 20, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2012 KeyBank [Member]	Dec. 31, 2011 KeyBank [Member]	Dec. 12, 2012 Common stock [Member]	Dec. 31, 2012 Common stock [Member] Maximum [Member]	Dec. 31, 2008 Series B Preferred Stock [Member]	Dec. 31, 2011 Series B Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Treasury stock, value									$ 344		$ 2,500
Common Share repurchase program								88
One-time deemed dividend due to repurchase				49
Elimination of dividends			31
Discount amortization			4
Return to U.S. Treasury above initial investment	367
Issuance of preferred stock to the U.S. Treasury										2,500
Warrants repurchased		$ 70			$ 70
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%