Securities - Additional Information (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2013 USD ($)	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($) security	Dec. 31, 2013 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Assets backed securities in available for sale portfolio | security		12	15
Assets backed securities wrapped by monoline insurance company | security		5	5
Value of asset backed securities backed by insurance company		$ 164	$ 183
Fair value of asset backed securities		173	226
Available-for-sale securities, backed by insurance company, accumulated unrecognized holding loss		29	23
Fair value of financial guarantee		75	89
Sold security at carrying value			76	$ 71
Recognized gains (losses) on securities	$ 8	$ 0	$ (9)	$ 8
Number of assets sold from held-to-maturity portfolio | security				6
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
Increase in credit losses for which an other-than-temporary impairment was previously recognized		$ 0
Other assets [Member]
Schedule of Available-for-sale Securities [Line Items]
Federal Home Loan Bank Stock		323	$ 108
Federal Reserve Bank Stock		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	$ 11	$ 0