Credit Quality (Summary of Loans Modified in a TDR) (Detail)		12 Months Ended
		Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	8,869	9,256	10,978
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 415,000,000	$ 413,000,000	$ 413,000,000
Increase (Decrease) to ALLL Upon Modification	[2]	13,000,000	13,000,000	32,000,000
Charge-offs Recognized Upon Modification	[2]	$ 9,000,000	$ 7,000,000	$ 4,000,000
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	54	75	74
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 200,000,000	$ 237,000,000	$ 183,000,000
Increase (Decrease) to ALLL Upon Modification	[2]	1,000,000	(5,000,000)	14,000,000
Charge-offs Recognized Upon Modification	[2]	$ 7,000,000	$ 6,000,000	$ 0
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-Occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	6	9	12
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 3,000,000	$ 8,000,000	$ 11,000,000
Increase (Decrease) to ALLL Upon Modification	[2]	(1,000,000)	5,000,000	0
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 0	$ 0
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	3	4	4
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 0	$ 0	$ 5,000,000
Increase (Decrease) to ALLL Upon Modification	[2]	0	0	2,000,000
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 0	$ 0
Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]		1	5
Recorded Investment in Loans Modified in a TDR During the Period	[2]		$ 4,000,000	$ 16,000,000
Increase (Decrease) to ALLL Upon Modification	[2]		0	0
Charge-offs Recognized Upon Modification	[2]		$ 0	$ 0
Residential Mortgage Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	1,128	830	924
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 168,000,000	$ 116,000,000	$ 137,000,000
Increase (Decrease) to ALLL Upon Modification	[2]	4,000,000	5,000,000	8,000,000
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 0	$ 0
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	111	150	219
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 7,000,000	$ 10,000,000	$ 15,000,000
Increase (Decrease) to ALLL Upon Modification	[2]	0	0	0
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 0	$ 0
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	84	102	221
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 0	$ 0	$ 3,000,000
Increase (Decrease) to ALLL Upon Modification	[2]	0	0	0
Charge-offs Recognized Upon Modification	[2]	$ 0	$ 0	$ 0
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period	[1],[2]	7,483	8,085	9,519
Recorded Investment in Loans Modified in a TDR During the Period	[2]	$ 37,000,000	$ 38,000,000	$ 43,000,000
Increase (Decrease) to ALLL Upon Modification	[2]	9,000,000	8,000,000	8,000,000
Charge-offs Recognized Upon Modification	[2]	$ 2,000,000	$ 1,000,000	$ 4,000,000

[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 .