Derivatives (Notional Amounts and Fair Values for All Derivative Instruments Included in the Consolidated Balance Sheets) (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value
Fair value - Derivative Assets	$ 735	$ 1,057
Fair value - Derivative Liabilities	499	666
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Derivatives, Fair Value
Fair value - Derivative Assets	310	345
Fair value - Derivative Liabilities	17	12
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges | Fair Value Hedging
Derivatives, Fair Value
Fair value - Derivative Assets	310	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	310	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	17	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	17	0
Nondesignated
Derivatives, Fair Value
Fair value - Derivative Assets	425	712
Fair value - Derivative Liabilities	482	654
Nondesignated | Risk Management and Other Business Purposes
Derivatives, Fair Value
Fair value - Derivative Assets	47	185
Fair value - Derivative Liabilities	155	133
Nondesignated | Risk Management and Other Business Purposes | Interest Rate Contract | Servicing Rights
Derivatives, Fair Value
Notional amount	11,452	10,522
Fair value - Derivative Assets	44	165
Fair value - Derivative Liabilities	17	39
Nondesignated | Risk Management and Other Business Purposes | Forward Contracts | Assets Held For Sale
Derivatives, Fair Value
Notional amount	2,297	1,823
Fair value - Derivative Assets	2	20
Fair value - Derivative Liabilities	2	3
Nondesignated | Risk Management and Other Business Purposes | Swap
Derivatives, Fair Value
Notional amount	1,753	1,300
Fair value - Derivative Assets	0	0
Fair value - Derivative Liabilities	136	91
Nondesignated | Risk Management and Other Business Purposes | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	118	111
Fair value - Derivative Assets	1	0
Fair value - Derivative Liabilities	0	0
Nondesignated | Customer Accommodation
Derivatives, Fair Value
Fair value - Derivative Assets	378	527
Fair value - Derivative Liabilities	327	521
Nondesignated | Customer Accommodation | Interest Rate Contract
Derivatives, Fair Value
Notional amount	41,065	33,431
Fair value - Derivative Assets	160	205
Fair value - Derivative Liabilities	121	210
Nondesignated | Customer Accommodation | Interest Rate Lock Commitments
Derivatives, Fair Value
Notional amount	652	701
Fair value - Derivative Assets	13	13
Fair value - Derivative Liabilities	0	1
Nondesignated | Customer Accommodation | Commodity Contract
Derivatives, Fair Value
Notional amount	2,800	2,095
Fair value - Derivative Assets	76	107
Fair value - Derivative Liabilities	76	106
Nondesignated | Customer Accommodation | TBAs
Derivatives, Fair Value
Notional amount	273
Fair value - Derivative Assets	0
Fair value - Derivative Liabilities	0
Nondesignated | Customer Accommodation | Foreign Exchange Contract
Derivatives, Fair Value
Notional amount	9,928	11,013
Fair value - Derivative Assets	129	202
Fair value - Derivative Liabilities	$ 130	$ 204