OTTI Losses on Available for Sale Securities (Detail) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Available-for-sale Securities	[1]	$ 31,444	$ 30,672
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held		$ 22		$ 24

[1] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $280 million and $0 million at September 30, 2017 and December 31, 2016, respectively.