Schedule of Financial Instruments Owned and Pledged as Collateral (Detail) - USD ($) $ in Millions		Mar. 31, 2019	Dec. 31, 2018
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of Repurchase Agreements Secured by Trading Assets		$ 1,300	$ 1,400
Trading Assets [Member] | Repurchase Agreements [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Security Owned and Pledged as Collateral, Fair Value	[1]	1,337	1,418
Trading Assets [Member] | Derivative [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Security Owned and Pledged as Collateral, Fair Value		43	22
Trading Assets [Member] | Equity Trading [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Security Owned and Pledged as Collateral, Fair Value		$ 40	$ 40

[1] Repurchase agreements secured by collateral totaled $1.3 billion and $1.4 billion at March 31, 2019 and December 31, 2018, respectively.