Fair Value Measurements (Fair Value Hierarchy For Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	$ 11,698	$ 10,689
Available for sale securities, equity securities	7,752	5,920
Separate accounts taxable fixed maturities	882	803
Total	20,350	17,434
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)	45	34
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Total	7,667	5,843
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)	45	34
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Total	12,683	11,586
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 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Total	0	5
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
Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	11,698	10,689
Fixed Maturities | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	6,401	5,710
Fixed Maturities | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	4,728	4,304
Fixed Maturities | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	301	288
Fixed Maturities | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	136	310
Fixed Maturities | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	104	67
Fixed Maturities | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	28	10
Fixed Maturities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	104	67
Fixed Maturities | Level 1 | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Fixed Maturities | Level 1 | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Fixed Maturities | Level 1 | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Fixed Maturities | Level 1 | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Fixed Maturities | Level 1 | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	104	67
Fixed Maturities | Level 1 | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Fixed Maturities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	11,594	10,617
Fixed Maturities | Level 2 | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	6,401	5,709
Fixed Maturities | Level 2 | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	4,728	4,300
Fixed Maturities | Level 2 | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	301	288
Fixed Maturities | Level 2 | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	136	310
Fixed Maturities | Level 2 | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Fixed Maturities | Level 2 | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	28	10
Fixed Maturities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	5
Fixed Maturities | Level 3 | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	1
Fixed Maturities | Level 3 | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	4
Fixed Maturities | Level 3 | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Fixed Maturities | Level 3 | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Fixed Maturities | Level 3 | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Fixed Maturities | Level 3 | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, debt securities	0	0
Equity Securities | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	7,518	5,742
Equity Securities | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	234	178
Equity Securities | Level 1 | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	7,518	5,742
Equity Securities | Level 1 | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	0	0
Equity Securities | Level 2 | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	0	0
Equity Securities | Level 2 | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	234	178
Equity Securities | Level 3 | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	0	0
Equity Securities | Level 3 | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Available for sale securities, equity securities	0	0
Taxable Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	855	791
Taxable Fixed Maturities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	0	0
Taxable Fixed Maturities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	855	791
Taxable Fixed Maturities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	$ 0	$ 0