Derivative Instruments- Fair Value of Derivative Contracts Falling under Early Termination Provisions in Net Liability Position (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
A-
Credit Derivatives [Line Items]
Potential close-out exposures (fair value)	$ 53	[1]
BBB
Credit Derivatives [Line Items]
Potential close-out exposures (fair value)	960	[1]
BB plus
Credit Derivatives [Line Items]
Potential close-out exposures (fair value)	2,643	[1]
A3
Credit Derivatives [Line Items]
Potential close-out exposures (fair value)	53	[1]
Baa2
Credit Derivatives [Line Items]
Potential close-out exposures (fair value)	960	[1]
Ba1
Credit Derivatives [Line Items]
Potential close-out exposures (fair value)	$ 2,643	[1]

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