Loans and Loans Held for Sale - Loans by Category (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Loans [Line Items]
Commercial, financial and agricultural	$ 21,979	$ 19,759	$ 17,848
Commercial mortgage	7,529	8,037	7,958
Construction	1,067	1,312	1,456
Total commercial real estate loans	8,596	9,349	9,414
Commercial lease financing	4,960	5,674	5,957
Total commercial loans	35,535	34,782	33,219
Real estate - residential mortgage	2,138	1,946	1,875
Home equity loan	10,177	9,764	9,912
Total residential - prime loans	12,315	11,710	11,787
Credit cards	710
Total consumer loans	15,884	14,793	14,976
Total loans	51,419	49,575	48,195
Other loan [Member]
Loans [Line Items]
Home equity loan	409	535	565
Key Community Bank [Member]
Loans [Line Items]
Home equity loan	9,768	9,229	9,347
Consumer other	1,313	1,192	1,187
Key Corporate Bank [Member]
Loans [Line Items]
Consumer other	1,546	1,891	2,002
Key Corporate Bank [Member] | Other loan [Member]
Loans [Line Items]
Consumer other	98	125	131
Key Corporate Bank [Member] | Marine loan [Member]
Loans [Line Items]
Consumer other	$ 1,448	$ 1,766	$ 1,871