Fair Value Measurements (details) - Fair Value Hierarchy (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	$ 63,690	$ 63,438
Fixed maturities [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	62,976	62,820
Fixed maturities [Member] | Level 1
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	2,139	2,025
Fixed maturities [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	60,640	60,565
Fixed maturities [Member] | Level 3
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	197	230
U.S. Treasury securities and obligations of U.S. Government and government agencies and authorities [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	2,146	2,008
U.S. Treasury securities and obligations of U.S. Government and government agencies and authorities [Member] | Level 1
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	2,103	1,991
U.S. Treasury securities and obligations of U.S. Government and government agencies and authorities [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	43	17
Obligations of states, municipalities and political subdivisions [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	39,180	39,535
Obligations of states, municipalities and political subdivisions [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	39,159	39,433
Obligations of states, municipalities and political subdivisions [Member] | Level 3
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	21	102
Debt securities issued by foreign governments [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	2,031	2,202
Debt securities issued by foreign governments [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	2,031	2,202
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	3,772	4,164
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	3,771	4,163
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] | Level 3
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	1	1
All other corporate bonds [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	15,810	14,876
All other corporate bonds [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	15,635	14,749
All other corporate bonds [Member] | Level 3
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	175	127
Redeemable preferred stock [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	37	35
Redeemable preferred stock [Member] | Level 1
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	36	34
Redeemable preferred stock [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	1	1
Equity securities [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	600	519
Equity securities [Member] | Level 1
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	520	412
Equity securities [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	80	107
Equity securities, common stock [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	398	304
Equity securities, common stock [Member] | Level 1
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	386	281
Equity securities, common stock [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	12	23
Equity securities, non-redeemable preferred stock [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	202	215
Equity securities, non-redeemable preferred stock [Member] | Level 1
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	134	131
Equity securities, non-redeemable preferred stock [Member] | Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	68	84
Other investments [Member]
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	114	99
Other investments [Member] | Level 1
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	43	42
Other investments [Member] | Level 3
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	71	57
Level 1
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	2,702	2,479
Level 2
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	60,720	60,672
Level 3
Level within the fair value hierarchy at which the Company's financial assets are measured
Total invested assets measured on a recurring basis	$ 268	$ 287