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Fair Value Measurements (Reconciliation Of Net Beginning And Ending Balances Recorded For Net Assets And Liabilities Classified As Level 3) (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Fair Value, Assets Measured On Recurring, Basis Unobservable Input Reconcilation Calculation Roll Forward [Abstract]        
Beginning balance   $ 2,764   $ 2,402
Total realized and unrealized gains included in net income (2) 1 (2)  
Purchases of PFD Preferred Stock   6,972 [1]   10,326 [1]
Redemptions of PFD Preferred Stock   (9,737) [1]   (12,730) [1]
Settlements of derivative instruments 2 (2) 2  
Ending balance   (2)   (2)
Unrealized gains or losses included in net income        
Unrealized gains or losses included in net income $ 0 $ (1) $ 0 $ (2)
[1] For information on PFD Preferred Stock, see Note 3. The fair value of our PFD Preferred Stock investment was measured using an income approach since the securities were not publicly traded; therefore, they were classified as Level 3 in the fair value hierarchy.