Derivatives (Notional Amounts and Fair Values for All Derivative Instruments Included in the Consolidated Balance Sheets) (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Derivatives, Fair Value
Fair value - Derivative Assets	$ 1,890	$ 1,852
Fair value - Derivative Liabilities	792	938
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Fair value - Derivative Assets	556	411
Fair value - Derivative Liabilities	0	2
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging
Derivatives, Fair Value
Fair value - Derivative Assets	473	372
Fair value - Derivative Liabilities	0	2
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging | Interest Rate Swap | Long-Term Debt
Derivatives, Fair Value
Notional amount	3,455	2,705
Fair value - Derivative Assets	473	372
Fair value - Derivative Liabilities	0	2
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Cash Flow Hedging
Derivatives, Fair Value
Fair value - Derivative Assets	83	39
Fair value - Derivative Liabilities	0	0
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Cash Flow Hedging | Interest Rate Swap | Commercial and Industrial Loans
Derivatives, Fair Value
Notional amount	4,475	5,475
Fair value - Derivative Assets	83	39
Fair value - Derivative Liabilities	0	0
Nondesignated
Derivatives, Fair Value
Fair value - Derivative Assets	1,334	1,441
Fair value - Derivative Liabilities	792	936
Nondesignated | Risk Management and Other Business Purposes
Derivatives, Fair Value
Fair value - Derivative Assets	657	504
Fair value - Derivative Liabilities	161	71
Nondesignated | Risk Management and Other Business Purposes | Interest Rate Contract | Servicing Rights
Derivatives, Fair Value
Notional amount	10,397	11,657
Fair value - Derivative Assets	332	239
Fair value - Derivative Liabilities	50	9
Nondesignated | Risk Management and Other Business Purposes | Forward Contracts | Assets Held For Sale
Derivatives, Fair Value
Notional amount	2,033	1,330
Fair value - Derivative Assets	0	3
Fair value - Derivative Liabilities	8	1
Nondesignated | Risk Management and Other Business Purposes | Warrant
Derivatives, Fair Value
Notional amount	438	369
Fair value - Derivative Assets	325	262
Fair value - Derivative Liabilities	0	0
Nondesignated | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional amount	1,378	1,292
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	103	61
Nondesignated | Risk Management and Other Business Purposes | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	168
Fair value - Derivative Assets	0
Fair value - Derivative Liabilities	0
Nondesignated | Customer Accommodation
Derivatives, Fair Value
Fair value - Derivative Assets	677	937
Fair value - Derivative Liabilities	631	865
Nondesignated | Customer Accommodation | Interest Rate Contract
Derivatives, Fair Value
Notional amount	32,218	29,889
Fair value - Derivative Assets	339	242
Fair value - Derivative Liabilities	346	249
Nondesignated | Customer Accommodation | Interest Rate Lock Commitments
Derivatives, Fair Value
Notional amount	1,215	721
Fair value - Derivative Assets	33	15
Fair value - Derivative Liabilities	0	0
Nondesignated | Customer Accommodation | Commodity Contract
Derivatives, Fair Value
Notional amount	1,800	2,464
Fair value - Derivative Assets	111	294
Fair value - Derivative Liabilities	99	276
Nondesignated | Customer Accommodation | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	12,545	16,243
Fair value - Derivative Assets	194	386
Fair value - Derivative Liabilities	$ 186	$ 340