Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	$ 952		$ 1,262		$ 952		$ 1,262
Fair Value Measured On Nonrecurring Basis Gains Losses	(139)		(398)		(339)		(849)
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	952		1,262		952		1,262
Loans Held For Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	13	[1]	60	[1]	13	[1]	60	[1]
Fair Value Measured On Nonrecurring Basis Gains Losses	(4)	[1]	(23)	[1]	(10)	[1]	(48)	[1]
Loans Held For Sale [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	13	[1]	60	[1]	13	[1]	60	[1]
Commercial And Industrial Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	79		155		79		155
Fair Value Measured On Nonrecurring Basis Gains Losses	(31)		(84)		(86)		(283)
Commercial And Industrial Loans [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	79		155		79		155
Commercial Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	59		145		59		145
Fair Value Measured On Nonrecurring Basis Gains Losses	(11)		(46)		(40)		(99)
Commercial Mortgage Loans [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	59		145		59		145
Commercial Construction
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	8		59		8		59
Fair Value Measured On Nonrecurring Basis Gains Losses	(5)		(14)		(21)		(52)
Commercial Construction | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	8		59		8		59
Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	679		662		679		662
Fair Value Measured On Nonrecurring Basis Gains Losses	(72)		(201)		(122)		(228)
Mortgage Servicing Rights | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	679		662		679		662
Other Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	114		181		114		181
Fair Value Measured On Nonrecurring Basis Gains Losses	(16)		(30)		(60)		(139)
Other Real Estate Owned [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements	$ 114		$ 181		$ 114		$ 181

[1] Includes commercial nonaccrual loans held for sale