Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012	Dec. 31, 2011
Financial assets:
Cash and due from banks	$ 2,186		$ 2,441		$ 2,235	$ 2,663
Held-to-maturity securities	283		284
Other short-term investments	2,286		2,421
Loans held for sale	2,560		2,856
Portfolio loans and leases:
Commercial and industrial loans	36,757		36,038
Commercial mortgage loans	8,766	[1]	9,103	[1]
Commercial construction loans	694		698
Commercial leases	3,568		3,549
Residential mortgage loans	12,091	[2]	12,017	[2]
Home equity	9,727		10,018
Automobile loans	11,741		11,972
Credit card	2,043		2,097
Other consumer loans and leases	289		290
Financial liabilities:
Federal funds purchased	386		901
Fair Value, Inputs, Level 2
Financial assets:
Loans held for sale	2,560		2,856
Carrying (Reported) Amount, Fair Value Disclosure
Financial assets:
Cash and due from banks	2,186		2,441
Other securities	844		844
Held-to-maturity securities	283		284
Other short-term investments	2,286		2,421
Loans held for sale	131		83
Portfolio loans and leases:
Commercial and industrial loans	35,970		35,236
Commercial mortgage loans	8,447		8,770
Commercial construction loans	670		665
Commercial leases	3,507		3,481
Residential mortgage loans	11,798		11,712	[3]
Home equity	9,583		9,875
Automobile loans	11,715		11,944
Credit card	1,955		2,010
Other consumer loans and leases	275		270
Unallocated allowance for loan and lease losses	(108)		(111)
Total portfolio loans and leases, net	83,812		83,852	[3]
Financial liabilities:
Deposits	91,624		89,517
Federal funds purchased	386		901
Other short-term borrowings	2,439		6,280
Long-term debt	8,320		7,085
Portion at Fair Value, Fair Value Disclosure
Financial assets:
Cash and due from banks	2,186		2,441
Other securities	844		844
Held-to-maturity securities	283		284
Other short-term investments	2,286		2,421
Loans held for sale	131		83
Portfolio loans and leases:
Commercial and industrial loans	37,621		36,496
Commercial mortgage loans	8,091		8,020
Commercial construction loans	537		505
Commercial leases	3,341		3,310
Residential mortgage loans	11,515		11,532	[3]
Home equity	9,527		9,798
Automobile loans	11,829		12,076
Credit card	2,083		2,139
Other consumer loans and leases	287		288
Total portfolio loans and leases, net	84,831		84,164	[3]
Financial liabilities:
Deposits	91,696		89,592
Federal funds purchased	386		901
Other short-term borrowings	2,439		6,280
Long-term debt	9,008		7,809
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks	2,186		2,441
Other short-term investments	2,286		2,421
Financial liabilities:
Federal funds purchased	386		901
Long-term debt	8,191		6,925
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2
Financial assets:
Other securities	844		844
Financial liabilities:
Deposits	91,696		89,592
Other short-term borrowings	2,439		6,280
Long-term debt	817		884
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3
Financial assets:
Held-to-maturity securities	283		284
Loans held for sale	131		83
Portfolio loans and leases:
Commercial and industrial loans	37,621		36,496
Commercial mortgage loans	8,091		8,020
Commercial construction loans	537		505
Commercial leases	3,341		3,310
Residential mortgage loans	11,515		11,532
Home equity	9,527		9,798
Automobile loans	11,829		12,076
Credit card	2,083		2,139
Other consumer loans and leases	287		288
Total portfolio loans and leases, net	$ 84,831		$ 84,164

[1] Includes $50 and $50 of commercial mortgage loans, $(13) and $(5) of ALLL, $1 and $3 of other assets from consolidated VIEs that are included in their respective captions above at March 31, 2013 and December 31, 2012, respectively. See Note 8.

[2] Includes $81 and $76 of residential mortgage loans measured at fair value at March 31, 2013 and December 31, 2012, respectively.

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