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Pension And Postretirement Benefits (Fair Value Assets Measured On Recurring Basis Unobservable Input (Level 3) Reconciliation) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Pension Assets [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year $ 2,106 $ 2,191
Realized gains (losses) (120) 227
Unrealized gains (losses) 399 209
Transfers in 73  
Transfers out (2)  
Purchases 68 196
Sales (210) (717)
Balance, end of year 2,314 2,106
Pension Assets [Member] | Equities [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 0 0
Realized gains (losses) 0 (1)
Unrealized gains (losses) 3 1
Transfers in (4)  
Transfers out 0  
Purchases 3 0
Sales (1) 0
Balance, end of year 1 0
Pension Assets [Member] | Fixed Income Funds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 44 51
Realized gains (losses) (17) (19)
Unrealized gains (losses) 19 16
Transfers in 0  
Transfers out (2)  
Purchases 0 1
Sales (4) (5)
Balance, end of year 40 44
Pension Assets [Member] | Real Estate And Real Assets [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 2,062 2,140
Realized gains (losses) (103) 247
Unrealized gains (losses) 377 192
Transfers in 77  
Transfers out 0  
Purchases 65 195
Sales (205) (712)
Balance, end of year 2,273 2,062
Postretirement Assets [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 15 2
Realized gains (losses) (2)  
Unrealized gains (losses) 2  
Transfers in 16 15
Transfers out   (1)
Sales (5) (1)
Balance, end of year 26 15
Postretirement Assets [Member] | Fixed Income Funds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 15 2
Realized gains (losses) (2)  
Unrealized gains (losses) 2  
Transfers in 16 15
Transfers out   (1)
Sales (5) (1)
Balance, end of year $ 26 $ 15