Derivative Financial Instruments - Credit-Risk Related Contingent Features (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013
Moodys Short Term Ratings P 1 [Member] | Moody's, A1 Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	$ 0
Moodys Short Term Ratings P 1 [Member] | Moody's, A2 Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	18
Moodys Short Term Ratings P 1 [Member] | Moody's, A3 Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	130
Moodys Short Term Ratings P 2 [Member] | Moody's, A1 Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	2
Moodys Short Term Ratings P 2 [Member] | Moody's, A2 Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	18
Moodys Short Term Ratings P 2 [Member] | Moody's, A3 Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	130
S And P Short Term Ratings A 1 [Member] | Standard & Poor's, AA- Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	0
S And P Short Term Ratings A 1 [Member] | Standard & Poor's, A+ Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	0
S And P Short Term Ratings A 1 [Member] | Standard & Poor's, A Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	16
S And P Short Term Rating A 1 [Member] | Standard & Poor's, AA- Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	5
S And P Short Term Rating A 1 [Member] | Standard & Poor's, A+ Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	5
S And P Short Term Rating A 1 [Member] | Standard & Poor's, A Rating [Member]
Credit Derivatives [Line Items]
Total Credit Rating Scenario of Derivatives	$ 21