Key Assumptions Used in Calculating Fair Value of Residential MSRs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Month	Dec. 31, 2010 Month
Mortgage Loans on Real Estate [Line Items]
Weighted average expected life	69	85
Constant prepayment speed	14.20%	10.10%
Discount rate	10.00%	10.00%
Primary mortgage rate to refinance	4.10%	5.00%
Current
Mortgage Loans on Real Estate [Line Items]
Cost to service per loan per year	53	53
30-59 days delinquent
Mortgage Loans on Real Estate [Line Items]
Cost to service per loan per year	103	103
60-89 days delinquent
Mortgage Loans on Real Estate [Line Items]
Cost to service per loan per year	203	203
90-119 days delinquent
Mortgage Loans on Real Estate [Line Items]
Cost to service per loan per year	303	303
Over 120 days delinquent
Mortgage Loans on Real Estate [Line Items]
Cost to service per loan per year	553	553