Derivative Financial Instruments - Credit-Risk Related Contingent Features (Detail) $ in Millions	Sep. 30, 2015 USD ($)
S&P Long Term Rating A plus [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	$ 95
S&P Long Term Rating A [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	142
Moody's Long Term Rating Aa3 [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	0
Moody's Long Term Rating A1 [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	$ 95