Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Detail) - USD ($) $ in Millions		Mar. 31, 2016		Dec. 31, 2015		Mar. 31, 2015	Dec. 31, 2014
Financial assets:
Cash and due from banks		$ 2,298	[1]	$ 2,540	[1]	$ 2,920	$ 3,091
Held-to-maturity securities, amortized cost	[2]	64		70
Other short-term investments		1,778		2,671
Loans held for sale	[3]	803		903
Portfolio loans and leases, net		92,310		91,310
Other securities, fair value	[4]	29,891		29,044
Held-to-maturity securities, fair value		64		70
Loans held for sale		600		519
Financial liabilities:
Deposits	[5]	102,475		103,205
Federal funds purchased		134		151
Other short-term borrowings		3,523		1,507
Long-term debt	[1],[6]	15,305		15,810
Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value		160				$ 126
Carrying (Reported) Amount, Fair Value Disclosure
Financial assets:
Cash and due from banks		2,298		2,540
Held-to-maturity securities, amortized cost		64		70
Other short-term investments		1,778		2,671
Loans held for sale		203		384
Unallocated Allowance For Loan And Lease Losses		(116)		(115)
Portfolio loans and leases at fair value		92,150		91,143
Financial liabilities:
Deposits		102,475		103,205
Federal funds purchased		134		151
Other short-term borrowings		3,523		1,507
Long-term debt		15,305		15,810
Carrying (Reported) Amount, Fair Value Disclosure | FHLB and FRB restricted stock holdings
Financial assets:
Other securities		604		604
Carrying (Reported) Amount, Fair Value Disclosure | Commercial and Industrial Loans | Commercial
Financial assets:
Portfolio loans and leases, net		42,736		41,479
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Mortgage Loans | Commercial
Financial assets:
Portfolio loans and leases, net		6,758		6,840
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Construction Loans | Commercial
Financial assets:
Portfolio loans and leases, net		3,404		3,190
Carrying (Reported) Amount, Fair Value Disclosure | Commercial Leases | Commercial
Financial assets:
Portfolio loans and leases, net		3,916		3,807
Carrying (Reported) Amount, Fair Value Disclosure | Residential Mortgage
Financial assets:
Portfolio loans and leases, net		13,637		13,449
Carrying (Reported) Amount, Fair Value Disclosure | Home Equity
Financial assets:
Portfolio loans and leases, net		8,050		8,234
Carrying (Reported) Amount, Fair Value Disclosure | Automobile Loan [Member]
Financial assets:
Portfolio loans and leases, net		11,087		11,453
Carrying (Reported) Amount, Fair Value Disclosure | Credit Card Receivables [Member]
Financial assets:
Portfolio loans and leases, net		2,039		2,160
Carrying (Reported) Amount, Fair Value Disclosure | Other Consumer Loans and Leases
Financial assets:
Portfolio loans and leases, net		639		646
Total Fair Value
Financial assets:
Cash and due from banks, fair value		2,298		2,540
Held-to-maturity securities, fair value		64		70
Other short term investments, fair value		1,778		2,671
Portfolio loans and leases at fair value		93,961		92,282
Financial liabilities:
Deposits, fair value		102,544		103,219
Federal funds purchased, fair value		134		151
Other short-term borrowings, fair value		3,523		1,507
Long term debt, fair value		15,904		16,228
Total Fair Value | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans held for sale		203		384
Total Fair Value | FHLB and FRB restricted stock holdings
Financial assets:
Other securities, fair value		604		604
Total Fair Value | Commercial and Industrial Loans | Commercial
Financial assets:
Portfolio loans and leases, net				41,802
Portfolio loans and leases at fair value		43,168
Total Fair Value | Commercial Mortgage Loans | Commercial
Financial assets:
Portfolio loans and leases, net		6,624		6,656
Total Fair Value | Commercial Construction Loans | Commercial
Financial assets:
Portfolio loans and leases, net		3,169		2,918
Total Fair Value | Commercial Leases | Commercial
Financial assets:
Portfolio loans and leases, net		3,675		3,533
Total Fair Value | Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value		14,588		14,061
Total Fair Value | Home Equity
Financial assets:
Portfolio loans and leases at fair value		8,855		8,948
Total Fair Value | Automobile Loan [Member]
Financial assets:
Portfolio loans and leases at fair value		10,834		11,170
Total Fair Value | Credit Card Receivables [Member]
Financial assets:
Portfolio loans and leases at fair value		2,432		2,551
Total Fair Value | Other Consumer Loans and Leases
Financial assets:
Portfolio loans and leases, net		616		643
Total Fair Value | Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks, fair value		2,298		2,540
Other short term investments, fair value		1,778		2,671
Financial liabilities:
Federal funds purchased, fair value		134		151
Long term debt, fair value		15,202		15,603
Total Fair Value | Fair Value, Inputs, Level 2
Financial liabilities:
Deposits, fair value		102,544		103,219
Other short-term borrowings, fair value		3,523		1,507
Long term debt, fair value		702		625
Total Fair Value | Fair Value, Inputs, Level 2 | FHLB and FRB restricted stock holdings
Financial assets:
Other securities, fair value		604		604
Total Fair Value | Fair Value, Inputs, Level 3
Financial assets:
Held-to-maturity securities, fair value		64		70
Portfolio loans and leases at fair value		93,961		92,282
Total Fair Value | Fair Value, Inputs, Level 3 | Non Fair Value Option Held For Sale Loans [Member]
Financial assets:
Loans held for sale		203		384
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial and Industrial Loans | Commercial
Financial assets:
Portfolio loans and leases, net				41,802
Portfolio loans and leases at fair value		43,168
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial Mortgage Loans | Commercial
Financial assets:
Portfolio loans and leases, net		6,624		6,656
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial Construction Loans | Commercial
Financial assets:
Portfolio loans and leases, net		3,169		2,918
Total Fair Value | Fair Value, Inputs, Level 3 | Commercial Leases | Commercial
Financial assets:
Portfolio loans and leases, net		3,675		3,533
Total Fair Value | Fair Value, Inputs, Level 3 | Residential Mortgage
Financial assets:
Portfolio loans and leases at fair value		14,588		14,061
Total Fair Value | Fair Value, Inputs, Level 3 | Home Equity
Financial assets:
Portfolio loans and leases at fair value		8,855		8,948
Total Fair Value | Fair Value, Inputs, Level 3 | Automobile Loan [Member]
Financial assets:
Portfolio loans and leases at fair value		10,834		11,170
Total Fair Value | Fair Value, Inputs, Level 3 | Credit Card Receivables [Member]
Financial assets:
Portfolio loans and leases at fair value		2,432		2,551
Total Fair Value | Fair Value, Inputs, Level 3 | Other Consumer Loans and Leases
Financial assets:
Portfolio loans and leases, net		$ 616		$ 643

[1] Includes $147 and $152 of cash and due from banks, $2,178 and $2,537 of portfolio loans and leases, $(27) and $(28) of ALLL, $11 and $14 of other assets, $4 and $3 of other liabilities, and $2,102 and $2,487 of long-term debt from consolidated VIEs that are included in their respective captions above at March 31, 2016 and December 31, 2015, respectively. For further information refer to Note 9.

[2] Fair value of $64 and $70 at March 31, 2016 and December 31, 2015, respectively.

[3] Includes $600 and $519 of residential mortgage loans held for sale measured at fair value at March 31, 2016 and December 31, 2015, respectively.

[4] Amortized cost of $28,838 and $28,678 at March 31, 2016 and December 31, 2015, respectively.

[5] Includes $331 and $628 of deposits held for sale at March 31, 2016 and December 31, 2015, respectively. For further information refer to Note 7.

[6] Upon adoption of ASU 2015-03 on January 1, 2016, the December 31, 2015 Condensed Consolidated Balance Sheets were adjusted to reflect the reclassification of $34 million of debt issuance costs from other assets to long-term debt. For further information refer to Note 3.