Credit Quality (Summary of Loans Modified in a TDR) (Detail) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2018 USD ($)	[3],[4]	Jun. 30, 2017 USD ($)		Jun. 30, 2018 USD ($)	[3],[4]	Jun. 30, 2017 USD ($)	[7]
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2,273	[1],[2]	2,430	[5],[6],[7],[8]	4,544	[1],[2]	4,489	[5],[6],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 166		$ 103	[7],[8]	$ 282		$ 240	[8]
Increase (Decrease) to ALLL Upon Modification	0		9	[7],[8]	16		13	[8]
Charge-offs Recognized Upon Modification	$ 1		$ 5	[7],[8]	$ 1		$ 7	[8]
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	13	[1],[2]	17	[5],[6],[7],[8]	25	[1],[2]	50	[5],[6],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 64		$ 56	[7],[8]	$ 135		$ 153	[8]
Increase (Decrease) to ALLL Upon Modification	(4)		1	[7],[8]	9		2	[8]
Charge-offs Recognized Upon Modification	0		$ 4	[7],[8]	$ 0		$ 6	[8]
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period			2	[5],[6],[7],[8]	2	[1],[2]	7	[5],[6],[8]
Recorded Investment in Loans Modified in a TDR During the Period			$ 6	[7],[8]	$ 0		$ 8	[8]
Increase (Decrease) to ALLL Upon Modification			5	[7],[8]	0		5	[8]
Charge-offs Recognized Upon Modification			$ 0	[7],[8]	$ 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		0	[1],[2]	2	[6]
Recorded Investment in Loans Modified in a TDR During the Period			$ 0	[7]	$ 0		$ 0
Increase (Decrease) to ALLL Upon Modification			0	[7]	0		0
Charge-offs Recognized Upon Modification	$ 0		$ 0	[7]	$ 0		$ 0
Residential Mortgage Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	537	[1],[2]	199	[5],[6],[7],[8]	784	[1],[2]	402	[5],[6],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 91		$ 28	[7],[8]	$ 124		$ 57	[8]
Increase (Decrease) to ALLL Upon Modification	2		1	[7],[8]	3		3	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[7],[8]	$ 0		$ 0	[8]
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	29	[1],[2]	44	[5],[6],[7],[8]	54	[1],[2]	75	[5],[6],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 2		$ 3	[7],[8]	$ 4		$ 5	[8]
Increase (Decrease) to ALLL Upon Modification	0		0	[7],[8]	0		0	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[7],[8]	$ 0		$ 0	[8]
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	19	[1],[2]	15	[5],[6],[7],[8]	39	[1],[2]	45	[5],[6],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 0	[7],[8]	$ 0		$ 0	[8]
Increase (Decrease) to ALLL Upon Modification	0		0	[7],[8]	0		0	[8]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[7],[8]	$ 0		$ 0	[8]
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	1,675	[1],[2]	2,152	[5],[6],[7],[8]	3,640	[1],[2]	3,908	[5],[6],[8]
Recorded Investment in Loans Modified in a TDR During the Period	$ 9		$ 10	[7],[8]	$ 19		$ 17	[8]
Increase (Decrease) to ALLL Upon Modification	2		2	[7],[8]	4		3	[8]
Charge-offs Recognized Upon Modification	$ 1		$ 1	[7],[8]	$ 1		$ 1	[8]

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

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

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

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