Mortgage Servicing Rights - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Transfers And Servicing Of Financial Assets [Abstract]
Company serviced residential mortgage loan for others	$ 223,900,000,000		$ 223,900,000,000		$ 215,600,000,000
Gain/Loss on the fair value of mortgage servicing rights and fair value changes of derivatives used to offset MSR	13,000,000	32,000,000	55,000,000	62,000,000
Loan servicing fees	$ 187,000,000	$ 174,000,000	$ 374,000,000	$ 345,000,000