|
Short-Term Investments (Components Of Short-Term Investments) (Details) (USD $)
In Millions, unless otherwise specified |
Jun. 30, 2012
|
Dec. 31, 2011
|
|---|---|---|
| Schedule of Investments [Line Items] | ||
| Short-term investments | $ 944 | $ 1,503 |
|
Canadian Province And Government Securities [Member]
|
||
| Schedule of Investments [Line Items] | ||
| Short-term investments | 644 | 1,155 |
|
U.S. Treasuries [Member]
|
||
| Schedule of Investments [Line Items] | ||
| Short-term investments | 300 | 201 |
|
Other
|
||
| Schedule of Investments [Line Items] | ||
| Short-term investments | $ 147 |