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Benefit Plans (Summary of the components of net periodic benefit cost recognized for pension plans) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Qualified [Member]
   
Defined Benefit Plan Disclosure [Line Items]    
Service cost $ 29 $ 26
Interest cost 25 23
Estimated return on plan assets (49) (49)
Net amortization and other 17 7
Net periodic benefit cost 22 7
Nonqualified [Member]
   
Defined Benefit Plan Disclosure [Line Items]    
Service cost 2 2
Interest cost 3 2
Estimated return on plan assets 0 0
Net amortization and other 1 1
Net periodic benefit cost $ 6 $ 5