Derivative Financial Instruments (Details 9) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
Moody's, Aa3 Rating [Member] | Moody's Short Term Ratings P-2 [Member]
Credit-Risk Related Contingent Features
Total Credit Rating Scenario of Derivatives	$ 2
Moody's, A1 Rating [Member] | Moody's, Short Term Ratings, P-1[Member]
Credit-Risk Related Contingent Features
Total Credit Rating Scenario of Derivatives	59
Moody's, A1 Rating [Member] | Moody's Short Term Ratings P-2 [Member]
Credit-Risk Related Contingent Features
Total Credit Rating Scenario of Derivatives	6
Moody's, A2 Rating [Member] | Moody's, Short Term Ratings, P-1[Member]
Credit-Risk Related Contingent Features
Total Credit Rating Scenario of Derivatives	261
Moody's, A2 Rating [Member] | Moody's Short Term Ratings P-2 [Member]
Credit-Risk Related Contingent Features
Total Credit Rating Scenario of Derivatives	261
S&P, AA- Rating [Member] | S&P Short Term Ratings A-1 [Member]
Credit-Risk Related Contingent Features
Total Credit Rating Scenario of Derivatives	48
S&P, A+ Rating [Member] | S&P Short Term Ratings A-1 [Member]
Credit-Risk Related Contingent Features
Total Credit Rating Scenario of Derivatives	101
S&P, A Rating [Member] | S&P Short Term Ratings A-1+ [Member]
Credit-Risk Related Contingent Features
Total Credit Rating Scenario of Derivatives	53
S&P, A Rating [Member] | S&P Short Term Ratings A-1 [Member]
Credit-Risk Related Contingent Features
Total Credit Rating Scenario of Derivatives	$ 303