Schedule of Financial Instruments Owned and Pledged as Collateral (Detail) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of Repurchase Agreements Secured by Trading Assets		$ 975	$ 928
Repurchase Agreements [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Trading Securities Pledged as Collateral	[1]	1,016	968
Derivative [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Trading Securities Pledged as Collateral		72	471
Equity Trading [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Trading Securities Pledged as Collateral		$ 41	$ 40

[1] Repurchase agreements secured by collateral totaled $975 million and $928 million at December 31, 2017 and 2016, respectively.