Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011		Dec. 31, 2010
Financial assets:
Cash and due from banks	$ 2,490	[1]	$ 2,663	[1]	$ 2,348	[1]	$ 2,159
Held-to-maturity securities	287		322		337
Other short-term investments	1,286	[1]	1,781	[1]	2,028	[1]
Loans held for sale	1,741		2,751		1,593
Portfolio loans and leases:
Commercial and industrial loans	33,344		30,783		29,258
Commercial mortgage loans	9,348	[1]	10,138	[1]	10,330	[1]
Commercial construction loans	672		1,020		1,213
Commercial leases	3,549		3,531		3,368
Residential mortgage loans	11,708	[2]	10,672	[2]	10,249	[2]
Home equity	10,238	[1]	10,719	[1]	10,920	[1]
Automobile loans	11,912	[1]	11,827	[1]	11,593	[1]
Credit card	1,994		1,978		1,878
Other consumer loans and leases	294		350		407
Financial liabilities:
Federal funds purchased	686		346		427
Fair Value, Inputs, Level 2
Financial assets:
Loans held for sale	1,741		2,751		1,593
Carrying (Reported) Amount, Fair Value Disclosure
Financial assets:
Cash and due from banks	2,490		2,663		2,348
Other securities	843		842		842
Held-to-maturity securities	287		322		337
Other short-term investments	1,286		1,781		2,028
Loans held for sale	61		203		247
Portfolio loans and leases:
Commercial and industrial loans	32,526		29,854		28,245
Commercial mortgage loans	8,989		9,697		9,857
Commercial construction loans	633		943		1,134
Commercial leases	3,478		3,451		3,284
Residential mortgage loans	11,400	[3]	10,380	[4]	9,954
Home equity	10,080		10,524		10,711
Automobile loans	11,884		11,784		11,536
Credit card	1,910		1,872		1,759
Other consumer loans and leases	274		329		384
Unallocated allowance for loan and lease losses	(116)		(136)		(149)
Total portfolio loans and leases, net	81,058	[3]	78,698	[4]	76,715
Financial liabilities:
Deposits	84,688		85,710		82,047
Federal funds purchased	686		346		427
Other short-term borrowings	5,503		3,239		4,894
Long-term debt	8,127		9,682		9,800
Portion at Fair Value, Fair Value Disclosure
Financial assets:
Cash and due from banks	2,490		2,663		2,348
Other securities	843		842		842
Held-to-maturity securities	287		322		337
Other short-term investments	1,286		1,781		2,028
Loans held for sale	61		203		247
Portfolio loans and leases:
Commercial and industrial loans	33,701		30,300		29,538
Commercial mortgage loans	8,259		8,870		9,167
Commercial construction loans	520		791		889
Commercial leases	3,355		3,237		3,131
Residential mortgage loans	11,350	[3]	9,978	[4]	9,516	[5]
Home equity	10,064		9,737		9,765
Automobile loans	11,825		11,747		11,575
Credit card	2,070		1,958		1,831
Other consumer loans and leases	292		346		430
Total portfolio loans and leases, net	81,436	[3]	76,964	[4]	75,842	[5]
Financial liabilities:
Deposits	84,779		85,599		82,196
Federal funds purchased	686		346		427
Other short-term borrowings	5,503		3,239		4,894
Long-term debt	9,030		10,197		10,199
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks	2,490
Other short-term investments	1,286
Financial liabilities:
Federal funds purchased	686
Long-term debt	6,973
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2
Financial assets:
Other securities	843
Financial liabilities:
Deposits	84,779
Other short-term borrowings	5,503
Long-term debt	2,057
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3
Financial assets:
Held-to-maturity securities	287
Loans held for sale	61
Portfolio loans and leases:
Commercial and industrial loans	33,701
Commercial mortgage loans	8,259
Commercial construction loans	520
Commercial leases	3,355
Residential mortgage loans	11,350
Home equity	10,064
Automobile loans	11,825
Credit card	2,070
Other consumer loans and leases	292
Total portfolio loans and leases, net	$ 81,436

[1] Includes $0, $30 and $35 of cash, $0, $7 and $7of other short-term investments, $50, $50 and $29 of commercial mortgage loans, $0, $223 and $228 of home equity loans, $0, $259 and $334 of automobile loans, ($2), ($10) and ($10) of ALLL, $3, $4 and $3 of other assets, $0, $4 and $5 of other liabilities, $0, $191and $270 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2012, December 31, 2011 and September 30, 2011, respectively. See Note 8.

[2] Includes $76, $65 and $62 of residential mortgage loans measured at fair value at September 30, 2012, December 31, 2011 and September 30, 2011, respectively.

[3] Excludes $76 of residential mortgage loans measured at fair value on a recurring basis.

[4] Excludes $65 of residential mortgage loans measured at fair value on a recurring basis.

[5] (a) Excludes $62 million of residential mortgage loans measured at fair value on a recurring basis.