Employee Retirement Benefits (Fair Value Hierarchy Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	$ 9,650	$ 9,460
Available for sale securities, equity securities	4,706	4,858
Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	45	52
Fixed Maturities | States, Municipalities and Political Subdivisions
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	32	33
Fixed Maturities | Corporate Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	13	19
Equity Securities | Common Stock
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	212	225
Debt And Equity Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	257	277
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	212	225
Level 1 | Debt And Equity Securities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, equity securities	212	225
Level 2 | Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	45	52
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	32	33
Level 2 | Fixed Maturities | Corporate Fixed Maturities
Schedule of Pension and Other Postretirment Plan Assets by Fair Value
Available for sale securities, debt securities	13	19
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	45	52
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