Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) security	Sep. 30, 2015 USD ($) security	Sep. 30, 2016 USD ($) security	Sep. 30, 2015 USD ($) security	Dec. 31, 2015 USD ($) security
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Assets backed securities in available for sale portfolio | security	12		12		12
Assets backed securities wrapped by monoline insurance company | security	5		5		5
Value of asset backed securities backed by insurance company	$ 159,000,000		$ 159,000,000		$ 164,000,000
Fair value of asset backed securities	563,000,000		563,000,000		173,000,000
Available-for-sale securities, backed by insurance company, accumulated unrecognized holding loss	32,000,000		32,000,000		29,000,000
Fair value of financial guarantee	$ 65,000,000		$ 65,000,000		75,000,000
Held-to-maturity Securities [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Asset backed securities with changes to other than temporary impairment estimates related to credit component | security	0	0	0	0
Increase in credit losses for which an other-than-temporary impairment was previously recognized	$ 0	$ 0	$ 0	$ 0
Other assets [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Federal Home Loan Bank Stock	383,000,000		383,000,000		323,000,000
Federal Reserve Bank Stock	$ 632,000,000		$ 632,000,000		$ 632,000,000