Fair Value Measurements (Fair Value Hierarchy For Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	$ 10,689	$ 10,699
Available for sale securities, equity securities	5,920	6,249
Separate accounts taxable fixed maturities	803	806
Total	17,434	17,774
Top Hat Savings Plan - Mutual Funds and Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Top Hat savings plan mutual funds and common equity (included in Other assets)	34	31
Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	10,689	10,699
Fixed Maturities | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	5,710	5,653
Fixed Maturities | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	4,304	4,465
Fixed Maturities | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	288	286
Fixed Maturities | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	310	254
Fixed Maturities | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	10	10
Fixed Maturities | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	67	31
Equity Securities | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	5,742	6,039
Equity Securities | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	178	210
Taxable Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	791	795
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Total	5,843	6,101
Level 1 | Top Hat Savings Plan - Mutual Funds and Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Top Hat savings plan mutual funds and common equity (included in Other assets)	34	31
Level 1 | Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	67	31
Level 1 | Fixed Maturities | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 1 | Fixed Maturities | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 1 | Fixed Maturities | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 1 | Fixed Maturities | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 1 | Fixed Maturities | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 1 | Fixed Maturities | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	67	31
Level 1 | Equity Securities | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	5,742	6,039
Level 1 | Equity Securities | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	0	0
Level 1 | Taxable Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Total	11,586	11,667
Level 2 | Top Hat Savings Plan - Mutual Funds and Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Top Hat savings plan mutual funds and common equity (included in Other assets)	0	0
Level 2 | Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	10,617	10,662
Level 2 | Fixed Maturities | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	5,709	5,652
Level 2 | Fixed Maturities | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	4,300	4,460
Level 2 | Fixed Maturities | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	288	286
Level 2 | Fixed Maturities | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	310	254
Level 2 | Fixed Maturities | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	10	10
Level 2 | Fixed Maturities | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 2 | Equity Securities | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	0	0
Level 2 | Equity Securities | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	178	210
Level 2 | Taxable Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	791	795
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Total	5	6
Level 3 | Top Hat Savings Plan - Mutual Funds and Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Top Hat savings plan mutual funds and common equity (included in Other assets)	0	0
Level 3 | Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	5	6
Level 3 | Fixed Maturities | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	1	1
Level 3 | Fixed Maturities | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	4	5
Level 3 | Fixed Maturities | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 3 | Fixed Maturities | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 3 | Fixed Maturities | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 3 | Fixed Maturities | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Level 3 | Equity Securities | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	0	0
Level 3 | Equity Securities | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	0	0
Level 3 | Taxable Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	$ 0	$ 0