Rollforward of Credit Losses Recognized in Earnings Related to Securities (Detail) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities	[1]	$ 31,358	$ 31,442
Ending balance		$ 0	$ 0

[1] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $151 million and $222 million at September 30, 2019 and December 31, 2018, respectively.