Securities - Additional Information (Detail) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) security	Jun. 30, 2014 USD ($) security	Jun. 30, 2015 USD ($) security	Jun. 30, 2014 USD ($) security	Dec. 31, 2014 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Assets backed securities in available for sale portfolio | security	14		14		15
Assets backed securities wrapped by monoline insurance company | security	5		5		5
Value of asset backed securities backed by insurance company	$ 176		$ 176		$ 183
Fair value of asset backed securities	204		204		226
Available-for-sale securities, backed by insurance company, accumulated unrecognized holding loss	22		22		23
Fair value of financial guarantee	$ 82		$ 82		89
Held-to-maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Asset backed securities with changes to other than temporary impairment estimates related to credit component | security	0	2	0	2
Increase in credit losses for which an other-than-temporary impairment was previously recognized	$ 0		$ 0
Other assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Federal Home Loan Bank Stock	331		331		108
Federal Reserve Bank Stock	632		632		$ 483
Other Revenues [Member] | Held-to-maturity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Increase in credit losses for which an other-than-temporary impairment was previously recognized	$ 0	$ 5	$ 0	$ 7