Credit Quality (Summary of Loans Modified in a TDR) (Detail) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2016 USD ($)	[1]	Sep. 30, 2015 USD ($)	[3]	Sep. 30, 2016 USD ($)	[1]	Sep. 30, 2015 USD ($)	[3]
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2,687	[2]	3,551	[4]	8,366	[2]	11,227	[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 112		$ 82		$ 347		$ 314
Increase (Decrease) to ALLL Upon Modification	14		13		30		21
Charge-offs Recognized Upon Modification	$ 1		$ 2		$ 3		$ 8
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	12	[2]	15	[4]	56	[2]	63	[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 41		$ 17		$ 158		$ 105
Increase (Decrease) to ALLL Upon Modification	10		7		19		7
Charge-offs Recognized Upon Modification	$ 0		$ 0		$ 0		$ 3
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	1	[2]	1	[4]	11	[2]	14	[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 1		$ 0		$ 9		$ 15
Increase (Decrease) to ALLL Upon Modification	0		0		(2)		(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	0	[2]	0	[4]	4	[2]	11	[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 0		$ 5		$ 7
Increase (Decrease) to ALLL Upon Modification	0		0		1		0
Charge-offs Recognized Upon Modification	$ 0		$ 0		$ 0		$ 0
Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	5	[2]	0	[4]	5	[2]	0	[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 16		$ 0		$ 16		$ 0
Increase (Decrease) to ALLL Upon Modification	0		0		0		0
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	240	[2]	301	[4]	745	[2]	855	[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 38		$ 44		$ 111		$ 121
Increase (Decrease) to ALLL Upon Modification	2		3		6		7
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	57	[2]	60	[4]	183	[2]	203	[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 5		$ 4		$ 12		$ 11
Increase (Decrease) to ALLL Upon Modification	0		0		0		(1)
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	52	[2]	98	[4]	188	[2]	357	[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 1		$ 2		$ 3		$ 6
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	2,320	[2]	3,076	[4]	7,174	[2]	9,724	[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 10		$ 15		$ 33		$ 49
Increase (Decrease) to ALLL Upon Modification	2		3		6		10
Charge-offs Recognized Upon Modification	$ 1		$ 2		$ 3		$ 5

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

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

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

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