Credit Quality (Summary of Loans Modified in a TDR) (Detail) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2017 USD ($)	[2]	Sep. 30, 2016 USD ($)		Sep. 30, 2017 USD ($)	[6]	Sep. 30, 2016 USD ($)
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2,353	[1]	2,687	[3],[4]	6,842	[5]	8,366	[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 120		$ 112	[4]	$ 360		$ 347	[8]
Increase (Decrease) to ALLL Upon Modification	(3)		14	[4]	10		30	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 1	[4]	$ 7		$ 3	[8]
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	17	[1]	12	[3],[4]	67	[5]	56	[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 73		$ 41	[4]	$ 226		$ 158	[8]
Increase (Decrease) to ALLL Upon Modification	(6)		10	[4]	(4)		19	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[4]	$ 6		$ 0	[8]
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	1	[1]	1	[3],[4]	8	[5]	11	[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 1	[4]	$ 8		$ 9	[8]
Increase (Decrease) to ALLL Upon Modification	0		0	[4]	5		(2)	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[4]	$ 0		$ 0	[8]
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	1	[1]			3	[5]	4	[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0				$ 0		$ 5	[8]
Increase (Decrease) to ALLL Upon Modification	0				0		1	[8]
Charge-offs Recognized Upon Modification	$ 0				$ 0		$ 0	[8]
Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period			5				5
Recorded Investment in Loans Modified in a TDR During the Period			$ 16				$ 16
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	247	[1]	240	[3],[4]	649	[5]	745	[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 35		$ 38	[4]	$ 92		$ 111	[8]
Increase (Decrease) to ALLL Upon Modification	1		2	[4]	4		6	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[4]	$ 0		$ 0	[8]
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	38	[1]	57	[3],[4]	113	[5]	183	[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 2		$ 5	[4]	$ 7		$ 12	[8]
Increase (Decrease) to ALLL Upon Modification	0		0	[4]	0		0	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[4]	$ 0		$ 0	[8]
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	28	[1]	52	[3],[4]	73	[5]	188	[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 1	[4]	$ 0		$ 3	[8]
Increase (Decrease) to ALLL Upon Modification	0		0	[4]	0		0	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[4]	$ 0		$ 0	[8]
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2,021	[1]	2,320	[3],[4]	5,929	[5]	7,174	[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 10		$ 10	[4]	$ 27		$ 33	[8]
Increase (Decrease) to ALLL Upon Modification	2		2	[4]	5		6	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 1	[4]	$ 1		$ 3	[8]

[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 .