Fair Value Measurements (Fair Value Hierarchy For Assets Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	$ 9,460	$ 9,121
Available for sale securities, equity securities	4,858	4,375
Separate accounts taxable fixed maturities	752	692
Total	15,067	14,192
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 equities (included in Other assets)	18	14
Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	9,460	9,121
Fixed Maturities | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	5,526	5,533
Fixed Maturities | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	3,443	3,211
Fixed Maturities | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	259	143
Fixed Maturities | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	208	200
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 | Convertibles and Bonds with Warrants Attached
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	7	17
Fixed Maturities | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	7	7
Equity Securities | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	4,679	4,213
Equity Securities | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	179	162
Taxable Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	731	682
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Total	4,704	4,234
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 equities (included in Other assets)	18	14
Level 1 | Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	7	7
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 | Convertibles and Bonds with Warrants Attached
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	7	7
Level 1 | Equity Securities | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	4,679	4,213
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
Available for sale securities, equity securities		53
Total	10,343	9,954
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 equities (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	9,435	9,112
Level 2 | Fixed Maturities | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	5,508	5,531
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	3,443	3,211
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	259	143
Level 2 | Fixed Maturities | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	208	200
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 | Convertibles and Bonds with Warrants Attached
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	7	17
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	177	160
Level 2 | Taxable Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	731	682
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities		0
Total	20	4
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 equities (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	18	2
Level 3 | Fixed Maturities | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	18	2
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	0	0
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 | Convertibles and Bonds with Warrants Attached
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	2	2
Level 3 | Taxable Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	$ 0	$ 0