Credit Quality (Summary of Loans Modified in a TDR) (Detail) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2017 USD ($)	[2]	Jun. 30, 2016 USD ($)	[4]	Jun. 30, 2017 USD ($)	[6]	Jun. 30, 2016 USD ($)	[8]
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2,430	[1]	2,669	[3]	4,489	[5]	5,679	[7]
Recorded Investment in Loans Modified in a TDR During the Period	$ 103		$ 119		$ 240		$ 235
Increase (Decrease) to ALLL Upon Modification	9		16		13		16
Charge-offs Recognized Upon Modification	$ 5		$ 1		$ 7		$ 2
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	17	[1]	20	[3]	50	[5]	44	[7]
Recorded Investment in Loans Modified in a TDR During the Period	$ 56		$ 61		$ 153		$ 117
Increase (Decrease) to ALLL Upon Modification	1		11		2		9
Charge-offs Recognized Upon Modification	$ 4		$ 0		$ 6		$ 0
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2	[1]	3	[3]	7	[5]	10	[7]
Recorded Investment in Loans Modified in a TDR During the Period	$ 6		$ 2		$ 8		$ 8
Increase (Decrease) to ALLL Upon Modification	5		0		5		(2)
Charge-offs Recognized Upon Modification	$ 0		$ 0		$ 0		$ 0
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	1	[1]	2	[3]	2	[5]	4	[7]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 5		$ 0		$ 5
Increase (Decrease) to ALLL Upon Modification	0		1		0		1
Charge-offs Recognized Upon Modification	$ 0		$ 0		$ 0		$ 0
Residential Mortgage Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	199	[1]	262	[3]	402	[5]	505	[7]
Recorded Investment in Loans Modified in a TDR During the Period	$ 28		$ 37		$ 57		$ 73
Increase (Decrease) to ALLL Upon Modification	1		2		3		4
Charge-offs Recognized Upon Modification	$ 0		$ 0		$ 0		$ 0
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	44	[1]	62	[3]	75	[5]	126	[7]
Recorded Investment in Loans Modified in a TDR During the Period	$ 3		$ 2		$ 5		$ 7
Increase (Decrease) to ALLL Upon Modification	0		0		0		0
Charge-offs Recognized Upon Modification	$ 0		$ 0		$ 0		$ 0
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	15	[1]	58	[3]	45	[5]	136	[7]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 1		$ 0		$ 2
Increase (Decrease) to ALLL Upon Modification	0		0		0		0
Charge-offs Recognized Upon Modification	$ 0		$ 0		$ 0		$ 0
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2,152	[1]	2,262	[3]	3,908	[5]	4,854	[7]
Recorded Investment in Loans Modified in a TDR During the Period	$ 10		$ 11		$ 17		$ 23
Increase (Decrease) to ALLL Upon Modification	2		2		3		4
Charge-offs Recognized Upon Modification	$ 1		$ 1		$ 1		$ 2

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

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

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

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

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

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

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

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