Guarantee Arrangements, Pledged Assets and Repurchase Agreements - Net Credit Derivative Positions (Detail) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Credit Derivatives [Line Items]
Net position, Carrying/Fair Value	[1]	$ 177	$ 115
Notional	[1]	5,995	5,634
Sell-protection credit derivative positions [Member]
Credit Derivatives [Line Items]
Carrying/Fair Value		(158)	303
Notional		42,543	42,328
Buy-protection credit derivative positions [Member]
Credit Derivatives [Line Items]
Carrying/Fair Value		335	(188)
Notional		$ 48,538	$ 47,962

[1] Positions are presented net in the table above to provide a complete analysis of our risk exposure and depict the way we manage our credit derivative portfolio. The offset of the sell-protection credit derivatives against the buy-protection credit derivatives may not be legally binding in the absence of master netting agreements with the same counterparty. Furthermore, the credit loss triggering events for individual sell protection credit derivatives may not be the same or occur in the same period as those of the buy protection credit derivatives thereby not providing an exact offset.