Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012	Dec. 31, 2011
Financial assets:
Cash and due from banks	$ 2,887	[1]	$ 2,441	[1]	$ 2,490	$ 2,663
Held-to-maturity securities	265	[2]	284	[2]
Other short-term investments	2,622		2,421
Loans held for sale	1,330	[3]	2,939	[3]
Portfolio loans and leases, net	85,554		83,928
Other securities, fair value	18,080	[4]	15,207	[4]
Held-to-maturity securities, fair value	265		284
Loans held for sale	1,298		2,856
Financial liabilities:
Deposits	94,126		89,517
Federal funds purchased	225		901
Other short-term borrowings	3,487		6,280
Long-term debt	8,098	[1]	7,085	[1]
Carrying (Reported) Amount, Fair Value Disclosure
Financial assets:
Cash and due from banks	2,887		2,441
Held-to-maturity securities	265		284
Other short-term investments	2,622		2,421
Unallocated Allowance For Loan And Lease Losses	(101)		(111)
Portfolio loans and leases at fair value	85,465	[5]	83,852	[6]
Financial liabilities:
Deposits	94,126		89,517
Federal funds purchased	225		901
Other short-term borrowings	3,487		6,280
Long-term debt	8,098		7,085
Carrying (Reported) Amount, Fair Value Disclosure | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans held for sale	32		83
Carrying (Reported) Amount, Fair Value Disclosure | FHLB and FRB restricted stock holdings
Financial assets:
Other securities	846		844
Carrying (Reported) Amount, Fair Value Disclosure | Commercial And Industrial Loans [Member]
Financial assets:
Portfolio loans and leases, net	37,440		35,236
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Mortgage Loans [Member]
Financial assets:
Portfolio loans and leases, net	7,813		8,770
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Construction
Financial assets:
Portfolio loans and leases, net	843		665
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Leases [Member]
Financial assets:
Portfolio loans and leases, net	3,509		3,481
Carrying (Reported) Amount, Fair Value Disclosure | Residential Mortgage
Financial assets:
Portfolio loans and leases, net	12,251	[5]	11,712	[6]
Carrying (Reported) Amount, Fair Value Disclosure | Home Equity
Financial assets:
Portfolio loans and leases, net	9,251		9,875
Carrying (Reported) Amount, Fair Value Disclosure | Automobile Loan
Financial assets:
Portfolio loans and leases, net	12,046		11,944
Carrying (Reported) Amount, Fair Value Disclosure | Credit Card Loan [Member]
Financial assets:
Portfolio loans and leases, net	2,070		2,010
Carrying (Reported) Amount, Fair Value Disclosure | Other Consumer Loans And Leases [Member]
Financial assets:
Portfolio loans and leases, net	343		270
Portion at Fair Value, Fair Value Disclosure
Financial assets:
Cash and due from banks, fair value	2,887		2,441
Held-to-maturity securities, fair value	265		284
Other short term investments, fair value	2,622		2,421
Portfolio loans and leases at fair value	85,523	[5]	84,164	[6]
Financial liabilities:
Deposits, fair value	94,157		89,592
Federal funds purchased, fair value	225		901
Other short-term borrowings, fair value	3,487		6,280
Long term debt, fair value	8,578		7,809
Portion at Fair Value, Fair Value Disclosure | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans held for sale	32		83
Portion at Fair Value, Fair Value Disclosure | FHLB and FRB restricted stock holdings
Financial assets:
Other securities	846
Other securities, fair value			844
Portion at Fair Value, Fair Value Disclosure | Commercial And Industrial Loans [Member]
Financial assets:
Portfolio loans and leases at fair value	38,987		36,496
Portion at Fair Value, Fair Value Disclosure | Commercial Mortgage Loans [Member]
Financial assets:
Portfolio loans and leases at fair value	7,309		8,020
Portion at Fair Value, Fair Value Disclosure | Commercial Construction
Financial assets:
Portfolio loans and leases at fair value	699		505
Portion at Fair Value, Fair Value Disclosure | Commercial Leases [Member]
Financial assets:
Portfolio loans and leases at fair value	3,248		3,310
Portion at Fair Value, Fair Value Disclosure | Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value	11,635	[5]	11,532	[6]
Portion at Fair Value, Fair Value Disclosure | Home Equity
Financial assets:
Portfolio loans and leases at fair value	9,179		9,798
Portion at Fair Value, Fair Value Disclosure | Automobile Loan
Financial assets:
Portfolio loans and leases at fair value	11,879		12,076
Portion at Fair Value, Fair Value Disclosure | Credit Card Loan [Member]
Financial assets:
Portfolio loans and leases at fair value	2,230		2,139
Portion at Fair Value, Fair Value Disclosure | Other Consumer Loans And Leases [Member]
Financial assets:
Portfolio loans and leases at fair value	357		288
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks, fair value	2,887		2,441
Other short term investments, fair value	2,622		2,421
Financial liabilities:
Federal funds purchased, fair value	225		901
Long term debt, fair value	7,943		6,925
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2
Financial liabilities:
Deposits, fair value	94,157		89,592
Other short-term borrowings, fair value	3,487		6,280
Long term debt, fair value	635		884
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | FHLB and FRB restricted stock holdings
Financial assets:
Other securities, fair value	846		844
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3
Financial assets:
Held-to-maturity securities, fair value	265		284
Portfolio loans and leases at fair value	85,523	[5]	84,164	[6]
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans held for sale	32		83
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Commercial And Industrial Loans [Member]
Financial assets:
Portfolio loans and leases at fair value	38,987		36,496
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Commercial Mortgage Loans [Member]
Financial assets:
Portfolio loans and leases at fair value	7,309		8,020
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Commercial Construction
Financial assets:
Portfolio loans and leases at fair value	699		505
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Commercial Leases [Member]
Financial assets:
Portfolio loans and leases at fair value	3,248		3,310
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value	11,635	[5]	11,532	[6]
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Home Equity
Financial assets:
Portfolio loans and leases at fair value	9,179		9,798
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Automobile Loan
Financial assets:
Portfolio loans and leases at fair value	11,879		12,076
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Credit Card Loan [Member]
Financial assets:
Portfolio loans and leases at fair value	2,230		2,139
Portion at Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3 | Other Consumer Loans And Leases [Member]
Financial assets:
Portfolio loans and leases at fair value	$ 357		$ 288

[1] Includes $53 and $0 of cash and due from banks, $50 and $50 of commercial mortgage loans, $1,145 and $0 of automobile loans, $(16) and $(5) of ALLL, $12 and $3 of other assets, $2 and $0 of other liabilities, and $1,198 and $0 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2013 and December 31, 2012, respectively. See Note 9.

[2] Fair value of $265 and $284 at September 30, 2013 and December 31, 2012, respectively.

[3] Includes $1,298 and $2,856 of residential mortgage loans held for sale measured at fair value at September 30, 2013 and December 31, 2012, respectively.

[4] Amortized cost of $17,665 and $14,571 at September 30, 2013 and December 31, 2012, respectively.

[5] Excludes $89 of residential mortgage loans measured at fair value on a recurring basis

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