Statement of Comprehensive Income (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Before-Tax Amount [Member]
      
Comprehensive Income Disclosure [Line Items]      
Net Income (Loss) $ 436 [1] $ 374 [1] $ 349 [1]
Other Comprehensive Income (Loss)      
Pension and other postretirement benefits   (1) [1] 3 [1]
Financial instruments     2 [1]
Total other comprehensive income (loss)   (1) [1] 5 [1]
Total Comprehensive Income (Loss) 436 [1] 373 [1] 354 [1]
Income Tax (Expense) Benefit [Member]
      
Other Comprehensive Income (Loss)      
Pension and other postretirement benefits   1 (1)
Financial instruments     (1)
Total other comprehensive income (loss)   1 (2)
Total Comprehensive Income (Loss)   1 (2)
Net-Of-Tax Amount [Member]
      
Comprehensive Income Disclosure [Line Items]      
Net Income (Loss) 436 374 349
Other Comprehensive Income (Loss)      
Pension and other postretirement benefits     2
Financial instruments     1
Total other comprehensive income (loss)     3
Total Comprehensive Income (Loss) 436 374 352
Noncontrolling Interest Member
      
Comprehensive Income Disclosure [Line Items]      
Net Income (Loss) 19 (16) 24
Other Comprehensive Income (Loss)      
Financial instruments (36) 7 (3)
Total other comprehensive income (loss) (36) 7 (3)
Total Comprehensive Income (Loss) (17) (9) 21
Equity Component [Member]
      
Comprehensive Income Disclosure [Line Items]      
Net Income (Loss) 455 358 373
Other Comprehensive Income (Loss)      
Pension and other postretirement benefits     2
Financial instruments (36) 7 (2)
Total other comprehensive income (loss) (36) 7  
Total Comprehensive Income (Loss) $ 419 $ 365 $ 373
[1] Except Net Income (Loss) and Total Comprehensive Income (Loss).