Derivatives (Notional Amounts and Fair Values for All Derivative Instruments Included in the Consolidated Balance Sheets) (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value
Fair value - Derivative Assets	$ 846	$ 1,057
Fair value - Derivative Liabilities	489	666
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Fair value - Derivative Assets	305	345
Fair value - Derivative Liabilities	18	12
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging
Derivatives, Fair Value
Fair value - Derivative Assets	305	323
Fair value - Derivative Liabilities	0	12
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging | Interest Rate Swap | Long-Term Debt
Derivatives, Fair Value
Notional amount	2,955	3,455
Fair value - Derivative Assets	305	323
Fair value - Derivative Liabilities	0	12
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Cash Flow Hedging
Derivatives, Fair Value
Fair value - Derivative Assets	0	22
Fair value - Derivative Liabilities	18	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	4,475
Fair value - Derivative Assets	0	22
Fair value - Derivative Liabilities	18	0
Nondesignated
Derivatives, Fair Value
Fair value - Derivative Assets	541	712
Fair value - Derivative Liabilities	471	654
Nondesignated | Risk Management and Other Business Purposes
Derivatives, Fair Value
Fair value - Derivative Assets	130	185
Fair value - Derivative Liabilities	124	133
Nondesignated | Risk Management and Other Business Purposes | Interest Rate Contract | Servicing Rights
Derivatives, Fair Value
Notional amount	10,602	10,522
Fair value - Derivative Assets	129	165
Fair value - Derivative Liabilities	22	39
Nondesignated | Risk Management and Other Business Purposes | Forward Contracts | Assets Held For Sale
Derivatives, Fair Value
Notional amount	1,630	1,823
Fair value - Derivative Assets	1	20
Fair value - Derivative Liabilities	5	3
Nondesignated | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional amount	1,481	1,300
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	97	91
Nondesignated | Risk Management and Other Business Purposes | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	110	111
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	0	0
Nondesignated | Customer Accommodation
Derivatives, Fair Value
Fair value - Derivative Assets	411	527
Fair value - Derivative Liabilities	347	521
Nondesignated | Customer Accommodation | Interest Rate Contract
Derivatives, Fair Value
Notional amount	35,882	33,431
Fair value - Derivative Assets	190	205
Fair value - Derivative Liabilities	144	210
Nondesignated | Customer Accommodation | Interest Rate Lock Commitments
Derivatives, Fair Value
Notional amount	780	701
Fair value - Derivative Assets	16	13
Fair value - Derivative Liabilities	0	1
Nondesignated | Customer Accommodation | Commodity Contract
Derivatives, Fair Value
Notional amount	2,145	2,095
Fair value - Derivative Assets	79	107
Fair value - Derivative Liabilities	80	106
Nondesignated | Customer Accommodation | TBAs
Derivatives, Fair Value
Notional amount	36
Fair value - Derivative Assets	0
Fair value - Derivative Liabilities	0
Nondesignated | Customer Accommodation | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	10,024	11,013
Fair value - Derivative Assets	126	202
Fair value - Derivative Liabilities	$ 123	$ 204