Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Detail) - USD ($) $ in Millions		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Financial assets:
Cash and due from banks		$ 2,540	[1]	$ 3,091	[1]	$ 3,178	$ 2,441
Held-to-maturity securities, amortized cost	[2]	70		187
Other short-term investments		2,671		7,914
Loans and leases held for sale	[3]	903		1,261
Portfolio loans and leases, net		91,310		88,762
Other securities, fair value	[4]	29,044		22,408
Held-to-maturity securities, fair value		70		187
Loans held for sale		519		561
Portfolio loans and leases at fair value		167		108
Financial liabilities:
Deposits	[5]	103,205		101,712
Federal funds purchased		151		144
Other short-term borrowings		1,507		1,556
Long-term debt	[1]	15,844		14,967
Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value		167		108
Carrying (Reported) Amount, Fair Value Disclosure
Financial assets:
Cash and due from banks		2,540		3,091
Other securities		604		600
Held-to-maturity securities, amortized cost		70		187
Other short-term investments		2,671		7,914
Loans and leases held for sale		384		700
Portfolio loans and leases, net		91,143		88,654
Unallocated Allowance for Loan and Lease Losses		(115)		(106)
Financial liabilities:
Deposits		103,205		101,712
Federal funds purchased		151		144
Other short-term borrowings		1,507		1,556
Long-term debt		15,844		14,967
Carrying (Reported) Amount, Fair Value Disclosure | Commercial and Industrial Loans | Commercial
Financial assets:
Portfolio loans and leases, net		41,479		40,092
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Mortgage Loans | Commercial
Financial assets:
Portfolio loans and leases, net		6,840		7,259
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Construction Loans | Commercial
Financial assets:
Portfolio loans and leases, net		3,190		2,052
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Leases | Commercial
Financial assets:
Portfolio loans and leases, net		3,807		3,675
Carrying (Reported) Amount, Fair Value Disclosure | Residential Mortgage
Financial assets:
Portfolio loans and leases, net		13,449		12,177
Carrying (Reported) Amount, Fair Value Disclosure | Home Equity
Financial assets:
Portfolio loans and leases, net		8,234		8,799
Carrying (Reported) Amount, Fair Value Disclosure | Automobile Loans
Financial assets:
Portfolio loans and leases, net		11,453		12,004
Carrying (Reported) Amount, Fair Value Disclosure | Credit Card
Financial assets:
Portfolio loans and leases, net		2,160		2,297
Carrying (Reported) Amount, Fair Value Disclosure | Other Consumer Loans and Leases
Financial assets:
Portfolio loans and leases, net		646		405
Total Fair Value
Financial assets:
Cash and due from banks, fair value		2,540		3,091
Other securities, fair value		604		600
Held-to-maturity securities, fair value		70		187
Other Short Term Investments Fair Value Disclosure		2,671		7,914
Portfolio loans and leases at fair value		92,282		89,041
Financial liabilities:
Deposits, fair value		103,219		101,715
Federal funds purchased, fair value		151		144
Other short-term borrowings, fair value		1,507		1,561
Long term debt, fair value		16,262		15,648
Total Fair Value | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans held for sale		384		700
Total Fair Value | Commercial and Industrial Loans | Commercial
Financial assets:
Portfolio loans and leases at fair value		41,802		40,781
Total Fair Value | Commercial Mortgage Loans | Commercial
Financial assets:
Portfolio loans and leases at fair value		6,656		6,878
Total Fair Value | Commercial Construction Loans | Commercial
Financial assets:
Portfolio loans and leases at fair value		2,918		1,735
Total Fair Value | Commercial Leases | Commercial
Financial assets:
Portfolio loans and leases at fair value		3,533		3,426
Total Fair Value | Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value		14,061		12,249
Total Fair Value | Home Equity
Financial assets:
Portfolio loans and leases at fair value		8,948		9,224
Total Fair Value | Automobile Loans
Financial assets:
Portfolio loans and leases at fair value		11,170		11,748
Total Fair Value | Credit Card
Financial assets:
Portfolio loans and leases at fair value		2,551		2,586
Total Fair Value | Other Consumer Loans and Leases
Financial assets:
Portfolio loans and leases at fair value		643		414
Total Fair Value | Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks, fair value		2,540		3,091
Other Short Term Investments Fair Value Disclosure		2,671		7,914
Financial liabilities:
Federal funds purchased, fair value		151		144
Long term debt, fair value		15,637		14,993
Total Fair Value | Fair Value, Inputs, Level 2
Financial assets:
Other securities, fair value		604		600
Financial liabilities:
Deposits, fair value		103,219		101,715
Other short-term borrowings, fair value		1,507		1,561
Long term debt, fair value		625		655
Total Fair Value | Fair Value, Inputs, Level 3
Financial assets:
Held-to-maturity securities, fair value		70		187
Portfolio loans and leases at fair value		92,282		89,041
Total Fair Value | Fair Value, Inputs, Level 3 | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans held for sale		384		700
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial and Industrial Loans | Commercial
Financial assets:
Portfolio loans and leases at fair value		41,802		40,781
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial Mortgage Loans | Commercial
Financial assets:
Portfolio loans and leases at fair value		6,656		6,878
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial Construction Loans | Commercial
Financial assets:
Portfolio loans and leases at fair value		2,918		1,735
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial Leases | Commercial
Financial assets:
Portfolio loans and leases at fair value		3,533		3,426
Total Fair Value | Fair Value, Inputs, Level 3 | Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value		14,061		12,249
Total Fair Value | Fair Value, Inputs, Level 3 | Home Equity
Financial assets:
Portfolio loans and leases at fair value		8,948		9,224
Total Fair Value | Fair Value, Inputs, Level 3 | Automobile Loans
Financial assets:
Portfolio loans and leases at fair value		11,170		11,748
Total Fair Value | Fair Value, Inputs, Level 3 | Credit Card
Financial assets:
Portfolio loans and leases at fair value		2,551		2,586
Total Fair Value | Fair Value, Inputs, Level 3 | Other Consumer Loans and Leases
Financial assets:
Portfolio loans and leases at fair value		$ 643		$ 414

[1] Includes $152 and $179 of cash and due from banks, $2,537 and $3,378 of portfolio loans and leases, $(28) and $(22) of ALLL, $20 and $25 of other assets, $3 and $5 of other liabilities and $2,493 and $3,434 of long-term debt from consolidated VIEs that are included in their respective captions above at December 31, 2015 and 2014, respectively. For further information, refer to Note 11.

[2] Fair value of $70 and $187 at December 31, 2015 and 2014, respectively.

[3] Includes $519 and $561 of residential mortgage loans held for sale measured at fair value at December 31, 2015 and 2014, respectively.

[4] Amortized cost of $28,678 and $21,677 at December 31, 2015 and 2014, respectively.

[5] Includes $628 and $0 of deposits held for sale at December 31, 2015 and 2014, respectively. For further information refer to Note 7.