Credit Quality (Summary of Loans Modified in a TDR) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)	[2]	Mar. 31, 2016 USD ($)	[4]
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2,059	[1]	3,010	[3]
Recorded Investment in Loans Modified in a TDR During the Period	$ 137		$ 116
Increase (Decrease) to ALLL Upon Modification	4		0
Charge-offs Recognized Upon Modification	$ 2		$ 1
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	33	[1]	24	[3]
Recorded Investment in Loans Modified in a TDR During the Period	$ 97		$ 56
Increase (Decrease) to ALLL Upon Modification	1		(2)
Charge-offs Recognized Upon Modification	$ 2		$ 0
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	5	[1]	7	[3]
Recorded Investment in Loans Modified in a TDR During the Period	$ 2		$ 6
Increase (Decrease) to ALLL Upon Modification	0		(2)
Charge-offs Recognized Upon Modification	$ 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]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 0
Increase (Decrease) to ALLL Upon Modification	0		0
Charge-offs Recognized Upon Modification	$ 0		$ 0
Residential Mortgage Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	203	[1]	243	[3]
Recorded Investment in Loans Modified in a TDR During the Period	$ 29		$ 36
Increase (Decrease) to ALLL Upon Modification	2		2
Charge-offs Recognized Upon Modification	$ 0		$ 0
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	31	[1]	64	[3]
Recorded Investment in Loans Modified in a TDR During the Period	$ 2		$ 5
Increase (Decrease) to ALLL Upon Modification	0		0
Charge-offs Recognized Upon Modification	$ 0		$ 0
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	30	[1]	78	[3]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 1
Increase (Decrease) to ALLL Upon Modification	0		0
Charge-offs Recognized Upon Modification	$ 0		$ 0
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	1,756	[1]	2,592	[3]
Recorded Investment in Loans Modified in a TDR During the Period	$ 7		$ 12
Increase (Decrease) to ALLL Upon Modification	1		2
Charge-offs Recognized Upon Modification	$ 0		$ 1

[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 .