Mortgage Servicing Rights - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Transfers And Servicing Of Financial Assets [Abstract]
Company serviced residential mortgage loan for others	$ 220,300,000,000		$ 215,600,000,000
Gain/Loss on the fair value of mortgage servicing rights and fair value changes of derivatives used to offset MSR	42,000,000	30,000,000
Loan servicing fees	$ 187,000,000	$ 171,000,000