Credit Quality (Summary of Loans Modified in a TDR) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)	[2]	Mar. 31, 2017 USD ($)
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2,271	[1]	2,059	[3],[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 117		$ 137	[4]
Increase (Decrease) to ALLL Upon Modification	16		4	[4]
Charge-offs Recognized Upon Modification	$ 0		$ 2	[4]
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	12	[1]	33	[3],[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 72		$ 97	[4]
Increase (Decrease) to ALLL Upon Modification	13		1	[4]
Charge-offs Recognized Upon Modification	$ 0		$ 2	[4]
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	2	[1]	5	[3],[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 2	[4]
Increase (Decrease) to ALLL Upon Modification	0		0	[4]
Charge-offs Recognized Upon Modification	0		$ 0	[4]
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period			1
Recorded Investment in Loans Modified in a TDR During the Period			$ 0
Increase (Decrease) to ALLL Upon Modification			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]	203	[3],[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 33		$ 29	[4]
Increase (Decrease) to ALLL Upon Modification	1		2	[4]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[4]
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	25	[1]	31	[3],[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 2		$ 2	[4]
Increase (Decrease) to ALLL Upon Modification	0		0	[4]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[4]
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	20	[1]	30	[3],[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 0		$ 0	[4]
Increase (Decrease) to ALLL Upon Modification	0		0	[4]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[4]
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	1,965	[1]	1,756	[3],[4]
Recorded Investment in Loans Modified in a TDR During the Period	$ 10		$ 7	[4]
Increase (Decrease) to ALLL Upon Modification	2		1	[4]
Charge-offs Recognized Upon Modification	$ 0		$ 0	[4]

[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 .