Changes in the Allowance for Loan Losses (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	$ 53	$ 45	$ 20
Charge-offs	(19)	(20)	(13)
Recoveries	2	1
Provision for loan losses	18	27	38
Balance at end of year	54	53	45
Residential real estate mortgages
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	38
Charge-offs	(11)
Recoveries	1
Provision for loan losses	12
Balance at end of year	40
Home equity lines of credit
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of year	15
Charge-offs	(8)
Recoveries	1
Provision for loan losses	6
Balance at end of year	$ 14