Employee Retirement Benefits (Fair Value Hierarchy Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	$ 10,085	$ 9,650
Available for sale securities, equity securities	5,334	4,706
Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	51	45
Fixed Maturities | States, Municipalities and Political Subdivisions
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	31	32
Fixed Maturities | Corporate Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	20	13
Equity Securities | Common Stock
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	253	212
Debt And Equity Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	304	257
Level 1 | 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 | 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 | Equity Securities | Common Stock
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	253	212
Level 1 | Debt And Equity Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	253	212
Level 2 | Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	51	45
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	31	32
Level 2 | Fixed Maturities | Corporate Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	20	13
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	51	45
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 | 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