OTTI Losses on Available for Sale Securities (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale Securities	[1]	$ 31,416	$ 30,672
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held		23	23	$ 25
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, No Previous Impairment		$ 1	$ 0	$ 1

[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.