Credit Quality (Summary of Subsequent Defaults) (Detail) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Financing Receivable, Modifications
Number of contracts	[1]	472	505	1,410	1,378
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 10	$ 10	$ 45	$ 29
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of contracts	[1]	3	1	7	4
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 1	$ 1	$ 17	$ 4
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-occupied
Financing Receivable, Modifications
Number of contracts	[1]	1		4
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 0		$ 1
Commercial Portfolio Segment | Commercial Mortgage Loans, Nonowner-Occupied
Financing Receivable, Modifications
Number of contracts	[1]		2		2
Recorded Investment in Loans Modified in a TDR During the Period	[1]		$ 0		$ 0
Commercial Portfolio Segment | Commercial Leases
Financing Receivable, Modifications
Number of contracts					2
Recorded Investment in Loans Modified in a TDR During the Period	[2],[3],[4]				$ 1
Residential Mortgage Loans
Financing Receivable, Modifications
Number of contracts	[1]	49	41	132	127
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 7	$ 6	$ 19	$ 18
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of contracts	[1]	2	3	13	11
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 0	$ 0	$ 2	$ 1
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of contracts	[1]	417	458	1,254	1,232
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 2	$ 2	$ 6	$ 5

[1] (a) Excludes all loans and leases held for sale and loans acquired with deteriorated credit quality.

[2] During both the three and nine months ended September 30, 2017 , no assets or liabilities were transferred between Level 1 and Level 2.

[3] During the year ended December 31, 2016 , no assets or liabilities were transferred between Level 1 and Level 2.

[4] 0