Credit Quality (Summary of the ALLL and Related Loans and Leases Classified by Portfolio Segment) (Parenthetical) (Detail) $ in Millions	3 Months Ended				12 Months Ended
	Mar. 31, 2017 USD ($)		Mar. 31, 2016 USD ($)		Dec. 31, 2016 USD ($)		Dec. 31, 2015 USD ($)
Financing Receivable, Allowance for Credit Losses
Allowance for loan and lease losses	$ 1,238	[1]	$ 1,295		$ 1,253	[2],[3]	$ 1,272
Portfolio loans and leases	$ 91,487	[4],[5]			91,955	[6],[7]
Number of contracts	2,059	[8],[9]	3,010	[10],[11]
Recorded investment	$ 1,770	[12]			1,901	[13]
Variable Interest Entity, Primary Beneficiary
Financing Receivable, Allowance for Credit Losses
Allowance for loan and lease losses	25				26
Commercial | Variable Interest Entity, Primary Beneficiary
Financing Receivable, Allowance for Credit Losses
Allowance for loan and lease losses	$ 18				$ 18
Number of contracts	5				5
Recorded investment	$ 26				$ 26
Leveraged Leases
Financing Receivable, Allowance for Credit Losses
Allowance for loan and lease losses	2				2
Portfolio loans and leases	703				701
Residential Mortgage Loans
Financing Receivable, Allowance for Credit Losses
Portfolio loans and leases at fair value	$ 141				$ 143

[1] Includes $ 2 related to leveraged leases at March 31, 2017 .

[2] Includes $ 2 related to leveraged leases at December 31, 2016 .

[3] Includes $ 85 and $ 85 of cash and due from banks, $ 1,015 and $ 1,216 of portfolio loans and leases , $ (25) and $ (26) of ALLL, $ 7 and $ 9 of other assets, $ 2 and $ 3 of other liabilities , and $ 883 and $ 1,094 of long-term debt from consolidated VIEs that are included in their respective captions above at March 31, 2017 and December 31, 2016 , respectively. For further information refer to Note 10 .

[4] Excludes $ 141 of residential mortgage loans measured at fair value, and includes $ 7 03 of leveraged leases, net of unearned income at March 31, 2017 .

[5] Excludes $ 141 of residential mortgage loans measured at fair value at March 31, 2017 .

[6] Excludes $ 143 of residential mortgage loans measured at fair value at December 31, 2016 .

[7] Excludes $ 143 of residential mortgage loans measured at fair value, and includes $ 701 of leveraged leases, net of unearned income at December 31, 2016 .

[8] Represents number of loans post-modification and excludes loans previously modified in a TDR .

[9] Excludes all loans and leases held for sale and loans acquired with deteriorated credit quality which were accounted for within a pool .

[10] Represents number of loans post-modification and excludes loans previously modified in a TDR .

[11] Excludes all loans and leases held for sale and loans acquired with deteriorated credit quality which were accounted for within a pool .

[12] Includes $ 277 , $ 642 and $ 308 , respectively, of commercial, residential mortgage and consumer portfolio TDRs on accrual status and $ 251 , $ 14 an d $ 46 , respectively, of commercial, residential mortgage and consumer portfolio TDRs on nonaccrual status at March 31, 2017 .

[13] Includes $ 322 , $ 635 and $ 323 , respectively, of commercial, residential mortgage and consumer portfolio TDR s on accrual status and $ 192 , $ 17 and $ 48 , respectively , of commercial, residential mortgage and consumer portfolio TDRs on nonaccrual status at December 31, 2016 .