Gross Realized Gains and Losses on Sales and OTTI on Securities Available for Sale (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities, Gross Realized Gains		$ 3	$ 4	$ 25
Available-for-sale Securities, Gross Realized Losses		(110)	0	(3)
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment		(1)	0	(1)
Gain (Loss) on Sale of Securities, Net		108	(4)	$ (21)
Available-for-sale Securities	[1]	$ 31,416	$ 30,672

[1] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $223 million and $0 million at December 31, 2017 and December 31, 2016, respectively.