Significant Inputs Considered in Determining the Measurement of Credit Losses Recognized in Earnings for Securities (Detail) - USD ($) $ in Millions		Mar. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Available-for-sale Securities	[1]	$ 31,127	$ 30,672
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investment [Line Items]
Available-for-sale Securities		$ 71	$ 74

[1] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $100 million and $0 million at March 31, 2017 and December 31, 2016, respectively.