Schedule of Financial Instruments Owned and Pledged as Collateral (Detail) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of Repurchase Agreements Secured by Trading Assets		$ 1,066	$ 975
Repurchase Agreements [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Trading Securities Pledged as Collateral	[1]	1,092	1,016
Derivative [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Trading Securities Pledged as Collateral		65	72
Equity Trading [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Trading Securities Pledged as Collateral		$ 40	$ 41

[1] Repurchase agreements secured by collateral totaled $1.1 billion and $975 million at June 30, 2018 and December 31, 2017, respectively.