Quarterly report pursuant to Section 13 or 15(d)

Tracking Stocks (Narrative) (Details)

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Tracking Stocks (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
0 Months Ended 3 Months Ended
Feb. 09, 2011
Mar. 31, 2012
Mar. 31, 2011
Nov. 28, 2011
Tracking Stocks        
Equity Conversion       0.88129
Reattribution Of Cash Between Tracking Stocks $ 264 $ 0 $ (264)