Credit Quality (Summary of Subsequent Defaults) (Detail) $ in Millions		12 Months Ended
		Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Financing Receivable, Modifications
Number of contracts	[1]	1,832	1,918	2,124
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 52	$ 39	$ 42
Commercial Portfolio Segment | Commercial and Industrial Loans
Financing Receivable, Modifications
Number of contracts	[1]	7	8	7
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 17	$ 5	$ 11
Commercial Portfolio Segment | Commercial Mortgage Loans, Owner-Occupied
Financing Receivable, Modifications
Number of contracts	[1]	4	2	3
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 1	$ 0	$ 1
Commercial Portfolio Segment | Commercial leases
Financing Receivable, Modifications
Number of contracts	[1]		2
Recorded Investment in Loans Modified in a TDR During the Period	[1]		$ 1
Residential Mortgage Loans
Financing Receivable, Modifications
Number of contracts	[1]	172	172	156
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 24	$ 25	$ 21
Consumer Portfolio Segment | Home Equity
Financing Receivable, Modifications
Number of contracts	[1]	16	17	15
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 2	$ 1	$ 1
Consumer Portfolio Segment | Automobile Loans
Financing Receivable, Modifications
Number of contracts	[1]		2	8
Recorded Investment in Loans Modified in a TDR During the Period	[1]		$ 0	$ 0
Consumer Portfolio Segment | Credit Card
Financing Receivable, Modifications
Number of contracts	[1]	1,633	1,715	1,935
Recorded Investment in Loans Modified in a TDR During the Period	[1]	$ 8	$ 7	$ 8

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