Investments (details) - Investment Information (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Investment disclosure details
Fixed maturities, amortized cost	$ 59,767	$ 60,170
Equity securities, cost	461	372
Fixed maturities, at fair value	62,976	62,820
Equity securities, at fair value	600	519
Continuous unrealized loss position less than 12 months, fair value	4,425	7,808
Continuous unrealized loss position less than 12 months, gross unrealized losses	62	187
Continuous unrealized loss position 12 months or longer, fair value	433	812
Continuous unrealized loss position 12 months or longer, gross unrealized losses	35	64
Continuous unrealized loss position, total, fair value	4,858	8,620
Continuous unrealized loss position, total, gross unrealized losses	97	251
Available-for-sale securities for which fair value is less than 80% of amortized cost, 3 months or less	4
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 3 months, 6 months or less	3
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 12 months	10
Available-for-sale securities for which fair value is less than 80% of amortized cost, total	17
Fixed maturities [Member]
Investment disclosure details
Fixed maturities, amortized cost	59,767	60,170
Gross unrealized gains	3,304	2,896
Gross unrealized losses	95	246
Fixed maturities, at fair value	62,976	62,820
Continuous unrealized loss position less than 12 months, fair value	4,369	7,760
Continuous unrealized loss position less than 12 months, gross unrealized losses	62	186
Continuous unrealized loss position 12 months or longer, fair value	394	760
Continuous unrealized loss position 12 months or longer, gross unrealized losses	33	60
Continuous unrealized loss position, total, fair value	4,763	8,520
Continuous unrealized loss position, total, gross unrealized losses	95	246
Available-for-sale securities for which fair value is less than 80% of amortized cost, 3 months or less	4
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 3 months, 6 months or less	3
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 12 months	10
Available-for-sale securities for which fair value is less than 80% of amortized cost, total	17
U.S. Treasury securities and obligations of U.S. Government and government agencies and authorities [Member]
Investment disclosure details
Fixed maturities, amortized cost	2,057	1,914
Gross unrealized gains	89	94
Fixed maturities, at fair value	2,146	2,008
Continuous unrealized loss position less than 12 months, fair value		155
Continuous unrealized loss position, total, fair value		155
Obligations of states, municipalities and political subdivisions [Member]
Investment disclosure details
Fixed maturities, amortized cost	37,229	38,064
Gross unrealized gains	1,987	1,626
Gross unrealized losses	36	155
Fixed maturities, at fair value	39,180	39,535
Continuous unrealized loss position less than 12 months, fair value	2,440	5,854
Continuous unrealized loss position less than 12 months, gross unrealized losses	30	149
Continuous unrealized loss position 12 months or longer, fair value	133	139
Continuous unrealized loss position 12 months or longer, gross unrealized losses	6	6
Continuous unrealized loss position, total, fair value	2,573	5,993
Continuous unrealized loss position, total, gross unrealized losses	36	155
Obligations of states, municipalities and political subdivisions, pre-refunded [Member]
Investment disclosure details
Fixed maturities, amortized cost	6,603	6,787
Gross unrealized gains	517	505
Gross unrealized losses	1	1
Fixed maturities, at fair value	7,119	7,291
Obligations of states, municipalities and political subdivisions, all other [Member]
Investment disclosure details
Fixed maturities, amortized cost	30,626	31,277
Gross unrealized gains	1,470	1,121
Gross unrealized losses	35	154
Fixed maturities, at fair value	32,061	32,244
Debt securities issued by foreign governments [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,980	2,156
Gross unrealized gains	52	50
Gross unrealized losses	1	4
Fixed maturities, at fair value	2,031	2,202
Continuous unrealized loss position less than 12 months, fair value	221	419
Continuous unrealized loss position less than 12 months, gross unrealized losses	1	4
Continuous unrealized loss position 12 months or longer, fair value		13
Continuous unrealized loss position, total, fair value	221	432
Continuous unrealized loss position, total, gross unrealized losses	1	4
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Investment disclosure details
Fixed maturities, amortized cost	3,529	3,952
Gross unrealized gains	259	248
Gross unrealized losses	16	36
Fixed maturities, at fair value	3,772	4,164
Continuous unrealized loss position less than 12 months, fair value	191	77
Continuous unrealized loss position less than 12 months, gross unrealized losses	4	1
Continuous unrealized loss position 12 months or longer, fair value	167	420
Continuous unrealized loss position 12 months or longer, gross unrealized losses	12	35
Continuous unrealized loss position, total, fair value	358	497
Continuous unrealized loss position, total, gross unrealized losses	16	36
Available-for-sale securities for which fair value is less than 80% of amortized cost, 3 months or less	3
Available-for-sale securities for which fair value is less than 80% of amortized cost, total	3
All other corporate bonds [Member]
Investment disclosure details
Fixed maturities, amortized cost	14,939	14,051
Gross unrealized gains	913	876
Gross unrealized losses	42	51
Fixed maturities, at fair value	15,810	14,876
Continuous unrealized loss position less than 12 months, fair value	1,517	1,255
Continuous unrealized loss position less than 12 months, gross unrealized losses	27	32
Continuous unrealized loss position 12 months or longer, fair value	94	185
Continuous unrealized loss position 12 months or longer, gross unrealized losses	15	19
Continuous unrealized loss position, total, fair value	1,611	1,440
Continuous unrealized loss position, total, gross unrealized losses	42	51
Other fixed maturities [Member]
Investment disclosure details
Available-for-sale securities for which fair value is less than 80% of amortized cost, 3 months or less	1
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 3 months, 6 months or less	3
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 12 months	10
Available-for-sale securities for which fair value is less than 80% of amortized cost, total	14
Redeemable preferred stock [Member]
Investment disclosure details
Fixed maturities, amortized cost	33	33
Gross unrealized gains	4	2
Fixed maturities, at fair value	37	35
Continuous unrealized loss position 12 months or longer, fair value		3
Continuous unrealized loss position, total, fair value		3
Equity securities [Member]
Investment disclosure details
Equity securities, cost	461	372
Gross unrealized gains	141	152
Gross unrealized losses	2	5
Equity securities, at fair value	600	519
Continuous unrealized loss position less than 12 months, fair value	56	48
Continuous unrealized loss position less than 12 months, gross unrealized losses		1
Continuous unrealized loss position 12 months or longer, fair value	39	52
Continuous unrealized loss position 12 months or longer, gross unrealized losses	2	4
Continuous unrealized loss position, total, fair value	95	100
Continuous unrealized loss position, total, gross unrealized losses	2	5
Equity securities, common stock [Member]
Investment disclosure details
Equity securities, cost	294	198
Gross unrealized gains	104	106
Equity securities, at fair value	398	304
Continuous unrealized loss position less than 12 months, fair value	44	3
Continuous unrealized loss position 12 months or longer, fair value		3
Continuous unrealized loss position, total, fair value	44	6
Equity securities, non-redeemable preferred stock [Member]
Investment disclosure details
Equity securities, cost	167	174
Gross unrealized gains	37	46
Gross unrealized losses	2	5
Equity securities, at fair value	202	215
Continuous unrealized loss position less than 12 months, fair value	12	45
Continuous unrealized loss position less than 12 months, gross unrealized losses		1
Continuous unrealized loss position 12 months or longer, fair value	39	49
Continuous unrealized loss position 12 months or longer, gross unrealized losses	2	4
Continuous unrealized loss position, total, fair value	51	94
Continuous unrealized loss position, total, gross unrealized losses	$ 2	$ 5