Mortgage Servicing Rights - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Transfers and Servicing of Financial Assets [Abstract]
Residential mortgage loans serviced for others including subserviced mortgages with no corresponding MSRs asset	$ 229,300			$ 229,300		$ 225,000
Gain/Loss on fair value changes of MSRs due to changes in valuation assumptions and derivatives used to economically hedge MSRs	12	$ 49		18	$ 200
Loan servicing fees	$ 182	$ 178		$ 539	$ 551
Gain related to excess servicing rights sold			$ 44