Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Detail) - USD ($) $ in Millions		Sep. 30, 2015		Dec. 31, 2014		Sep. 30, 2014	Dec. 31, 2013
Financial assets:
Cash and due from banks		$ 2,455	[1]	$ 3,091	[1]	$ 3,125	$ 3,178
Held-to-maturity securities, amortized cost	[2]	157		187
Other short-term investments		1,994		7,914
Loans and leases held for sale	[3]	994		1,261
Portfolio loans and leases, net		92,313		88,762
Other securities, fair value	[4]	28,799		22,408
Held-to-maturity securities, fair value		157		187
Loans held for sale		617		561
Financial liabilities:
Deposits	[5]	100,893		101,712
Federal funds purchased		132		144
Other short-term borrowings		4,904		1,556
Long-term debt	[1]	15,527		14,967
Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value		173				$ 109
Carrying (Reported) Amount, Fair Value Disclosure
Financial assets:
Cash and due from banks		2,455		3,091
Held-to-maturity securities, amortized cost		157		187
Other short-term investments		1,994		7,914
Unallocated Allowance For Loan And Lease Losses		(114)		(106)
Portfolio loans and leases at fair value		92,140		88,654
Financial liabilities:
Deposits		100,893		101,712
Federal funds purchased		132		144
Other short-term borrowings		4,904		1,556
Long-term debt		15,527		14,967
Carrying (Reported) Amount, Fair Value Disclosure | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans and leases held for sale		377		700
Carrying (Reported) Amount, Fair Value Disclosure | FHLB and FRB restricted stock holdings
Financial assets:
Other securities		603		600
Carrying (Reported) Amount, Fair Value Disclosure | Commercial and Industrial Loans | Commercial
Financial assets:
Portfolio loans and leases, net		42,315		40,092
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Mortgage Loans | Commercial
Financial assets:
Portfolio loans and leases, net		6,936		7,259
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Construction Loans | Commercial
Financial assets:
Portfolio loans and leases, net		3,076		2,052
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Leases | Commercial
Financial assets:
Portfolio loans and leases, net		3,853		3,675
Carrying (Reported) Amount, Fair Value Disclosure | Residential Mortgage
Financial assets:
Portfolio loans and leases, net		13,121		12,177
Carrying (Reported) Amount, Fair Value Disclosure | Home Equity
Financial assets:
Portfolio loans and leases, net		8,357		8,799
Carrying (Reported) Amount, Fair Value Disclosure | Automobile Loan [Member]
Financial assets:
Portfolio loans and leases, net		11,785		12,004
Carrying (Reported) Amount, Fair Value Disclosure | Credit Card Receivables [Member]
Financial assets:
Portfolio loans and leases, net		2,133		2,297
Carrying (Reported) Amount, Fair Value Disclosure | Other Consumer Loans and Leases
Financial assets:
Portfolio loans and leases, net		678		405
Total Fair Value
Financial assets:
Cash and due from banks, fair value		2,455		3,091
Held-to-maturity securities, fair value		157		187
Other short term investments, fair value		1,994		7,914
Portfolio loans and leases at fair value		93,766		89,041
Financial liabilities:
Deposits, fair value		100,929		101,715
Federal funds purchased, fair value		132		144
Other short-term borrowings, fair value		4,905		1,561
Long term debt, fair value		16,119		15,648
Total Fair Value | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans and leases held for sale		377		700
Total Fair Value | FHLB and FRB restricted stock holdings
Financial assets:
Other securities, fair value		603		600
Total Fair Value | Commercial and Industrial Loans | Commercial
Financial assets:
Portfolio loans and leases, net				40,781
Portfolio loans and leases at fair value		42,845
Total Fair Value | Commercial Mortgage Loans | Commercial
Financial assets:
Portfolio loans and leases, net		6,731		6,878
Total Fair Value | Commercial Construction Loans | Commercial
Financial assets:
Portfolio loans and leases, net		2,801		1,735
Total Fair Value | Commercial Leases | Commercial
Financial assets:
Portfolio loans and leases, net		3,620		3,426
Total Fair Value | Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value		13,752		12,249
Total Fair Value | Home Equity
Financial assets:
Portfolio loans and leases at fair value		9,261		9,224
Total Fair Value | Automobile Loan [Member]
Financial assets:
Portfolio loans and leases at fair value		11,593		11,748
Total Fair Value | Credit Card Receivables [Member]
Financial assets:
Portfolio loans and leases at fair value		2,486		2,586
Total Fair Value | Other Consumer Loans and Leases
Financial assets:
Portfolio loans and leases, net		677		414
Total Fair Value | Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks, fair value		2,455		3,091
Other short term investments, fair value		1,994		7,914
Financial liabilities:
Federal funds purchased, fair value		132		144
Long term debt, fair value		15,464		14,993
Total Fair Value | Fair Value, Inputs, Level 2
Financial liabilities:
Deposits, fair value		100,929		101,715
Other short-term borrowings, fair value		4,905		1,561
Long term debt, fair value		655		655
Total Fair Value | Fair Value, Inputs, Level 2 | FHLB and FRB restricted stock holdings
Financial assets:
Other securities, fair value		603		600
Total Fair Value | Fair Value, Inputs, Level 3
Financial assets:
Held-to-maturity securities, fair value		157		187
Portfolio loans and leases at fair value		93,766		89,041
Total Fair Value | Fair Value, Inputs, Level 3 | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans and leases held for sale		377		700
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial and Industrial Loans | Commercial
Financial assets:
Portfolio loans and leases, net				40,781
Portfolio loans and leases at fair value		42,845
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial Mortgage Loans | Commercial
Financial assets:
Portfolio loans and leases, net		6,731		6,878
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial Construction Loans | Commercial
Financial assets:
Portfolio loans and leases, net		2,801		1,735
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial Leases | Commercial
Financial assets:
Portfolio loans and leases, net		3,620		3,426
Total Fair Value | Fair Value, Inputs, Level 3 | Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value		13,752		12,249
Total Fair Value | Fair Value, Inputs, Level 3 | Home Equity
Financial assets:
Portfolio loans and leases at fair value		9,261		9,224
Total Fair Value | Fair Value, Inputs, Level 3 | Automobile Loan [Member]
Financial assets:
Portfolio loans and leases at fair value		11,593		11,748
Total Fair Value | Fair Value, Inputs, Level 3 | Credit Card Receivables [Member]
Financial assets:
Portfolio loans and leases at fair value		2,486		2,586
Total Fair Value | Fair Value, Inputs, Level 3 | Other Consumer Loans and Leases
Financial assets:
Portfolio loans and leases, net		$ 677		$ 414

[1] Includes $137 and $179 of cash and due from banks, $2,179 and $3,378 of portfolio loans and leases, $(27) and $(22) of ALLL, $18 and $25 of other assets, $3 and $5 of other liabilities, and $2,136 and $3,434 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2015 and December 31, 2014, respectively. For further information refer to Note 11.

[2] Fair value of $157 and $187 at September 30, 2015 and December 31, 2014, respectively.

[3] Includes $617 and $561 of residential mortgage loans held for sale measured at fair value at September 30, 2015 and December 31, 2014, respectively.

[4] Amortized cost of $27,986 and $21,677 at September 30, 2015 and December 31, 2014, respectively.

[5] Includes $665 and $0 of deposits held for sale at September 30, 2015 and December 31, 2014, respectively. For further information refer to Note 7.