Mortgage Servicing Rights - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Servicing Assets at Fair Value [Line Items]
Company serviced residential mortgage loan for others	$ 211,300,000,000		$ 211,300,000,000		$ 191,100,000,000
Gain/Loss on the fair value of mortgage servicing rights and fair value changes of derivatives used to offset MSR	10,000,000	7,000,000	72,000,000	151,000,000
Loan servicing fees	$ 181,000,000	$ 166,000,000	$ 526,000,000	$ 483,000,000