Revolving Credit Facilities Schedule of Short term debt (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2012
|
Dec. 31, 2011
|
Dec. 31, 2010
|
|
Short-term Debt [Line Items] | |||
Average daily amount of short-term debt outstanding | $ 4 | $ 2 | $ 9 |
Weighted daily average interest rate | 0.40% | 0.40% | 0.40% |
Maximum amount outstanding during the year | $ 44 | $ 44 | $ 51 |