Fair Value Measurements - Fair Value Hierarchy Level within which Fair Value of Financial and Non-Financial Assets has Been Recorded (Detail) (Fair Value, Measurements, Nonrecurring [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	$ 227		$ 256
Fair Value Assets, Measured on Non-Recurring Basis, Gain Loss Included in Revenue	4	(13)
Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	28		24
Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	8		10
Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	191		222
Residential Mortgage [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	74		77
Fair Value Assets, Measured on Non-Recurring Basis, Gain Loss Included in Revenue	3	(2)
Residential Mortgage [Member] | Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	0		0
Residential Mortgage [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	8		10
Residential Mortgage [Member] | Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	66		67
Impaired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	125		155
Fair Value Assets, Measured on Non-Recurring Basis, Gain Loss Included in Revenue	(1)	(11)
Impaired loans [Member] | Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	0		0
Impaired loans [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	0
Impaired loans [Member] | Level 3 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	125		155
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	28		24
Fair Value Assets, Measured on Non-Recurring Basis, Gain Loss Included in Revenue	2	0
Commercial real estate [Member] | Level 1 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	28		24
Commercial real estate [Member] | Level 2 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	$ 0		$ 0