Offsetting Assets and Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Offsetting Asset and Liabilities [Line Items]
Potential net fair value positions elected to offset	$ (239)	$ 104
Receivables
Offsetting Asset and Liabilities [Line Items]
Potential net fair value positions elected to offset		89
Other Assets
Offsetting Asset and Liabilities [Line Items]
Potential net fair value positions elected to offset		15
Current liabilities: Other
Offsetting Asset and Liabilities [Line Items]
Potential net fair value positions elected to offset	(209)
Other liabilities and deferred credits: Other
Offsetting Asset and Liabilities [Line Items]
Potential net fair value positions elected to offset	$ (30)