Credit Quality (Summary of Loans Modified in a TDR) (Detail) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018 USD ($)		Sep. 30, 2017 USD ($)		Sep. 30, 2018 USD ($)		Sep. 30, 2017 USD ($)
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period		1,803		2,353		6,347		6,842
Recorded Investment in Loans Modified in a TDR During the Period		$ 86		$ 120		$ 368		$ 360
Increase (Decrease) to ALLL Upon Modification		(4)		(3)		12		10
Charge-offs Recognized Upon Modification		$ 7		$ 0		$ 8		$ 7
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period		16	[1],[2],[3],[4]	17	[5],[6],[7],[8]	41	[1],[2],[3],[4]	67	[5],[6],[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period		$ 52	[3],[4]	$ 73	[7],[8]	$ 187	[3],[4]	$ 226	[7],[8]
Increase (Decrease) to ALLL Upon Modification		(7)	[3],[4]	(6)	[7],[8]	2	[3],[4]	(4)	[7],[8]
Charge-offs Recognized Upon Modification		7	[3],[4]	$ 0	[7],[8]	$ 7	[3],[4]	$ 6	[7],[8]
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period				1	[5],[6],[7],[8]	2	[1],[2],[3],[4]	8	[5],[6],[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period				$ 0	[7],[8]	$ 0	[3],[4]	$ 8	[7],[8]
Increase (Decrease) to ALLL Upon Modification				0	[7],[8]	0	[3],[4]	5	[7],[8]
Charge-offs Recognized Upon Modification				$ 0	[7],[8]	$ 0	[3],[4]	$ 0	[7],[8]
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period				1				3	[6],[7]
Recorded Investment in Loans Modified in a TDR During the Period	[7]			$ 0				$ 0
Increase (Decrease) to ALLL Upon Modification	[7]			0				0
Charge-offs Recognized Upon Modification		$ 0	[3],[4]	$ 0	[7]			$ 0	[7]
Residential Mortgage Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period		185		247		969		649
Recorded Investment in Loans Modified in a TDR During the Period		$ 24		$ 35		$ 148		$ 92
Increase (Decrease) to ALLL Upon Modification		1		1		4		4
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		30	[1],[2],[3],[4]	38	[5],[6],[7],[8]	84	[1],[2],[3],[4]	113	[5],[6],[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period		$ 2	[3],[4]	$ 2	[7],[8]	$ 6	[3],[4]	$ 7	[7],[8]
Increase (Decrease) to ALLL Upon Modification		0	[3],[4]	0	[7],[8]	0	[3],[4]	0	[7],[8]
Charge-offs Recognized Upon Modification		$ 0	[3],[4]	$ 0	[7],[8]	$ 0	[3],[4]	$ 0	[7],[8]
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period		25	[1],[2],[3],[4]	28	[5],[6],[7],[8]	64	[1],[2],[3],[4]	73	[5],[6],[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period		$ 0	[3],[4]	$ 0	[7],[8]	$ 0	[3],[4]	$ 0	[7],[8]
Increase (Decrease) to ALLL Upon Modification		0	[3],[4]	0	[7],[8]	0	[3],[4]	0	[7],[8]
Charge-offs Recognized Upon Modification		$ 0	[3],[4]	$ 0	[7],[8]	$ 0	[3],[4]	$ 0	[7],[8]
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of Loans Modified in a TDR During the Period		1,547	[1],[2],[3],[4]	2,021	[5],[6],[7],[8]	5,187	[1],[2],[3],[4]	5,929	[5],[6],[7],[8]
Recorded Investment in Loans Modified in a TDR During the Period		$ 8	[3],[4]	$ 10	[7],[8]	$ 27	[3],[4]	$ 27	[7],[8]
Increase (Decrease) to ALLL Upon Modification		2	[3],[4]	2	[7],[8]	6	[3],[4]	5	[7],[8]
Charge-offs Recognized Upon Modification		$ 0	[3],[4]	$ 0	[7],[8]	$ 1	[3],[4]	$ 1	[7],[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 .