Employee Retirement Benefits (Fair Value Hierarchy Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	$ 10,689	$ 10,699
Available for sale securities, equity securities	5,920	6,249
Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	71	65
Fixed Maturities | States, Municipalities and Political Subdivisions
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	29	31
Fixed Maturities | Corporate Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	37	34
Fixed Maturities | United States Government
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	5
Equity Securities | Common Stock
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	215	262
Debt And Equity Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	286	327
Level 1 | Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	5	0
Level 1 | Fixed Maturities | States, Municipalities and Political Subdivisions
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	0	0
Level 1 | Fixed Maturities | Corporate Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	0	0
Level 1 | Fixed Maturities | United States Government
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	5
Level 1 | Equity Securities | Common Stock
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	215	262
Level 1 | Debt And Equity Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	220	262
Level 2 | Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	66	65
Level 2 | Fixed Maturities | States, Municipalities and Political Subdivisions
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	29	31
Level 2 | Fixed Maturities | Corporate Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	37	34
Level 2 | Fixed Maturities | United States Government
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	0
Level 2 | Equity Securities | Common Stock
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	0	0
Level 2 | Debt And Equity Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	66	65
Level 3 | Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	0	0
Level 3 | Fixed Maturities | States, Municipalities and Political Subdivisions
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	0	0
Level 3 | Fixed Maturities | Corporate Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	0	0
Level 3 | Fixed Maturities | United States Government
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	0
Level 3 | Equity Securities | Common Stock
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	0	0
Level 3 | Debt And Equity Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	$ 0	$ 0