Fair Value Measurements (Fair Value Hierarchy For Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	$ 12,338	$ 11,698
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	8,856	7,752
Separate accounts taxable fixed maturities	952	882
Total	22,148	20,350
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)	51	45
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Total	8,712	7,667
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)	51	45
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Total	13,436	12,683
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	0
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
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	12,338	11,698
Fixed Maturities | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	6,895	6,401
Fixed Maturities | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	4,997	4,728
Fixed Maturities | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	285	301
Fixed Maturities | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	120	104
Fixed Maturities | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	29	28
Fixed Maturities | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	12	136
Fixed Maturities | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	120	104
Fixed Maturities | Level 1 | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 1 | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 1 | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 1 | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	120	104
Fixed Maturities | Level 1 | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 1 | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	12,218	11,594
Fixed Maturities | Level 2 | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	6,895	6,401
Fixed Maturities | Level 2 | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	4,997	4,728
Fixed Maturities | Level 2 | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	285	301
Fixed Maturities | Level 2 | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 2 | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	29	28
Fixed Maturities | Level 2 | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	12	136
Fixed Maturities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 3 | Corporate Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 3 | States, Municipalities and Political Subdivisions
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 3 | Commercial Mortgage Backed Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 3 | United States Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 3 | Foreign Government
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Fixed Maturities | Level 3 | Government-Sponsored Enterprises
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Fixed maturities, at fair value (amortized cost: 2020—$11,312; 2019—$11,108)	0	0
Equity Securities | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	8,541	7,518
Equity Securities | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	315	234
Equity Securities | Level 1 | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	8,541	7,518
Equity Securities | Level 1 | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	0	0
Equity Securities | Level 2 | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	0	0
Equity Securities | Level 2 | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	315	234
Equity Securities | Level 3 | Common Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	0	0
Equity Securities | Level 3 | Nonredeemable Preferred Equities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Equity securities, at fair value (cost: 2020—$3,927; 2019—$3,581)	0	0
Taxable Fixed Maturities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	903	855
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	903	855
Taxable Fixed Maturities | Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis
Separate accounts taxable fixed maturities	$ 0	$ 0