v3.19.3.a.u2
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, 2019
Dec. 31, 2018
Pension Assets [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year $ 11,333 $ 2,293
Realized gains (losses) 64 120
Unrealized gains (losses) 103 (239)
Transfers in 147 9,425
Transfers out (6) (5)
Purchases 235 93
Sales (237) (354)
Balance, end of year 11,639 11,333
Pension Assets [Member] | Equities [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 8,750 4
Realized gains (losses) 0 0
Unrealized gains (losses) 58 (408)
Transfers in 8 9,158
Transfers out 0 (4)
Purchases 0 0
Sales 0 0
Balance, end of year 8,816 8,750
Pension Assets [Member] | Fixed Income Funds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 4 2
Realized gains (losses) 0 0
Unrealized gains (losses) 0 (1)
Transfers in 5 1
Transfers out (6) (1)
Purchases 7 8
Sales (4) (5)
Balance, end of year 6 4
Pension Assets [Member] | Real Estate And Real Assets [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 2,579 2,287
Realized gains (losses) 64 120
Unrealized gains (losses) 45 170
Transfers in 134 266
Transfers out 0 0
Purchases 228 85
Sales (233) (349)
Balance, end of year 2,817 2,579
Postretirement Assets [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 13 5
Transfers in 28 9
Transfers out (1) (1)
Purchases   1
Sales (8) (1)
Balance, end of year 32 13
Postretirement Assets [Member] | Equities [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 1 0
Transfers in 0 1
Transfers out 0 0
Purchases   0
Sales (1) 0
Balance, end of year 0 1
Postretirement Assets [Member] | Fixed Income Funds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 12 5
Transfers in 28 8
Transfers out (1) (1)
Purchases   1
Sales (7) (1)
Balance, end of year 32 12
Postretirement Assets [Member] | Real Estate And Real Assets [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Balance, beginning of year 0 0
Transfers in 0 0
Transfers out 0 0
Purchases   0
Sales 0 0
Balance, end of year $ 0 $ 0