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, 2018 USD ($)		Mar. 31, 2017 USD ($)		Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)	[2],[3]
Financing Receivable, Allowance for Credit Losses
Allowance for loan and lease losses	$ 1,138	[1],[2]	$ 1,238		$ 1,196	[2],[3]	$ 1,253
Portfolio loans and leases	$ 91,834	[4],[5]			91,833	[6],[7]
Number of contracts	2,271	[8],[9]	2,059	[10],[11]
Recorded investment	$ 1,547	[12]			1,545	[13]
Variable Interest Entity, Primary Beneficiary
Financing Receivable, Allowance for Credit Losses
Allowance for loan and lease losses	6				$ 6
Commercial | Variable Interest Entity, Primary Beneficiary
Financing Receivable, Allowance for Credit Losses
Number of contracts					5
Leveraged Leases
Financing Receivable, Allowance for Credit Losses
Allowance for loan and lease losses	1				$ 1
Portfolio loans and leases	670				674
Residential Mortgage Loans
Financing Receivable, Allowance for Credit Losses
Portfolio loans and leases at fair value	$ 136				$ 137

[1] Includes $ 1 related to leveraged leases at March 31, 2018 .

[2] Includes $ 66 and $ 62 of other short-term investments , $ 1,135 and $ 1,297 of portfolio loans and leases, $ (6) and $ (6) of ALLL, $ 6 and $ 7 of other assets, $ 2 and $ 2 of other liabilities, and $ 1,031 and $ 1,190 of long-term debt from consolidated VIEs that are included in their respe ctive captions above at March 31, 2018 and December 31, 2017 , respectively. For further information refer to Note 9 .

[3] Includes $ 1 related to leveraged leases at December 31, 2017 .

[4] Excludes $ 136 of residential mortgage loans measured at fair value and includes $ 670 of leveraged leases, net of unearned income at March 31, 2018 .

[5] Excludes $ 136 of residential mortgage loans measured at fair value at March 31, 2018 .

[6] Excludes $ 137 of residential mortga ge loans measured at fair value and includes $ 674 of leveraged leases, net of unearned income at December 31, 2017 .

[7] Excludes $ 137 of residential mortgage loans measured at fair value at December 31, 2017 .

[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 $ 249 , $ 654 and $ 262 , respectively, of commercial, residential mortgage and consumer portfolio TDRs on accrual status and $ 154 , $ 12 an d $ 46 , respectively, of commercial, re sidential mortgage and consumer portfolio TDRs on nonaccrual status at March 31, 2018 .

[13] Includes $ 249 , $ 652 and $ 275 , respectively, of commercial, residential mortgage and consumer portfolio TDR s on accrual status and $ 150 , $ 13 and $ 45 , respectively , of commercial, residential mortgage and consumer portfolio TDRs on nonaccrual status at December 31, 2017 .