Investments (details) - Investment Information (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Investment disclosure details
Fixed maturities, amortized cost	$ 60,056	$ 60,170
Equity securities, cost	467	372
Fixed maturities, at fair value	64,000	62,820
Equity securities, at fair value	570	519
Continuous unrealized loss position less than 12 months, fair value	3,528	7,808
Continuous unrealized loss position less than 12 months, gross unrealized losses	73	187
Continuous unrealized loss position 12 months or longer, fair value	360	812
Continuous unrealized loss position 12 months or longer, gross unrealized losses	35	64
Continuous unrealized loss position, total, fair value	3,888	8,620
Continuous unrealized loss position, total, gross unrealized losses	108	251
Available-for-sale securities for which fair value is less than 80% of amortized cost, 3 months or less	5
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 3 months, 6 months or less	2
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less	4
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 12 months	9
Available-for-sale securities for which fair value is less than 80% of amortized cost, total	20
Fixed maturities [Member]
Investment disclosure details
Fixed maturities, amortized cost	60,056	60,170
Gross unrealized gains	4,042	2,896
Gross unrealized losses	98	246
Fixed maturities, at fair value	64,000	62,820
Continuous unrealized loss position less than 12 months, fair value	3,391	7,760
Continuous unrealized loss position less than 12 months, gross unrealized losses	65	186
Continuous unrealized loss position 12 months or longer, fair value	325	760
Continuous unrealized loss position 12 months or longer, gross unrealized losses	33	60
Continuous unrealized loss position, total, fair value	3,716	8,520
Continuous unrealized loss position, total, gross unrealized losses	98	246
Available-for-sale securities for which fair value is less than 80% of amortized cost, 3 months or less	5
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 3 months, 6 months or less	2
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less	4
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 12 months	9
Available-for-sale securities for which fair value is less than 80% of amortized cost, total	20
U.S. Treasury securities and obligations of U.S. Government and government agencies and authorities [Member]
Investment disclosure details
Fixed maturities, amortized cost	2,125	1,914
Gross unrealized gains	106	94
Fixed maturities, at fair value	2,231	2,008
Continuous unrealized loss position less than 12 months, fair value	520	155
Continuous unrealized loss position, total, fair value	520	155
Obligations of states, municipalities and political subdivisions [Member]
Investment disclosure details
Fixed maturities, amortized cost	36,730	38,064
Gross unrealized gains	2,555	1,626
Gross unrealized losses	10	155
Fixed maturities, at fair value	39,275	39,535
Continuous unrealized loss position less than 12 months, fair value	731	5,854
Continuous unrealized loss position less than 12 months, gross unrealized losses	5	149
Continuous unrealized loss position 12 months or longer, fair value	115	139
Continuous unrealized loss position 12 months or longer, gross unrealized losses	5	6
Continuous unrealized loss position, total, fair value	846	5,993
Continuous unrealized loss position, total, gross unrealized losses	10	155
Obligations of states, municipalities and political subdivisions, pre-refunded [Member]
Investment disclosure details
Fixed maturities, amortized cost	6,599	6,787
Gross unrealized gains	533	505
Gross unrealized losses	1	1
Fixed maturities, at fair value	7,131	7,291
Obligations of states, municipalities and political subdivisions, all other [Member]
Investment disclosure details
Fixed maturities, amortized cost	30,131	31,277
Gross unrealized gains	2,022	1,121
Gross unrealized losses	9	154
Fixed maturities, at fair value	32,144	32,244
Debt securities issued by foreign governments [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,921	2,156
Gross unrealized gains	81	50
Gross unrealized losses		4
Fixed maturities, at fair value	2,002	2,202
Continuous unrealized loss position less than 12 months, fair value	54	419
Continuous unrealized loss position less than 12 months, gross unrealized losses		4
Continuous unrealized loss position 12 months or longer, fair value		13
Continuous unrealized loss position, total, fair value	54	432
Continuous unrealized loss position, total, gross unrealized losses		4
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Investment disclosure details
Fixed maturities, amortized cost	3,367	3,952
Gross unrealized gains	270	248
Gross unrealized losses	19	36
Fixed maturities, at fair value	3,618	4,164
Continuous unrealized loss position less than 12 months, fair value	292	77
Continuous unrealized loss position less than 12 months, gross unrealized losses	8	1
Continuous unrealized loss position 12 months or longer, fair value	137	420
Continuous unrealized loss position 12 months or longer, gross unrealized losses	11	35
Continuous unrealized loss position, total, fair value	429	497
Continuous unrealized loss position, total, gross unrealized losses	19	36
All other corporate bonds [Member]
Investment disclosure details
Fixed maturities, amortized cost	15,880	14,051
Gross unrealized gains	1,026	876
Gross unrealized losses	69	51
Fixed maturities, at fair value	16,837	14,876
Continuous unrealized loss position less than 12 months, fair value	1,794	1,255
Continuous unrealized loss position less than 12 months, gross unrealized losses	52	32
Continuous unrealized loss position 12 months or longer, fair value	73	185
Continuous unrealized loss position 12 months or longer, gross unrealized losses	17	19
Continuous unrealized loss position, total, fair value	1,867	1,440
Continuous unrealized loss position, total, gross unrealized losses	69	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	5
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 3 months, 6 months or less	2
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less	4
Available-for-sale securities for which fair value is less than 80% of amortized cost, greater than 12 months	9
Available-for-sale securities for which fair value is less than 80% of amortized cost, total	20
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	467	372
Gross unrealized gains	113	152
Gross unrealized losses	10	5
Equity securities, at fair value	570	519
Continuous unrealized loss position less than 12 months, fair value	137	48
Continuous unrealized loss position less than 12 months, gross unrealized losses	8	1
Continuous unrealized loss position 12 months or longer, fair value	35	52
Continuous unrealized loss position 12 months or longer, gross unrealized losses	2	4
Continuous unrealized loss position, total, fair value	172	100
Continuous unrealized loss position, total, gross unrealized losses	10	5
Equity securities, common stock [Member]
Investment disclosure details
Equity securities, cost	300	198
Gross unrealized gains	83	106
Gross unrealized losses	7
Equity securities, at fair value	376	304
Continuous unrealized loss position less than 12 months, fair value	79	3
Continuous unrealized loss position less than 12 months, gross unrealized losses	7
Continuous unrealized loss position 12 months or longer, fair value		3
Continuous unrealized loss position, total, fair value	79	6
Continuous unrealized loss position, total, gross unrealized losses	7
Equity securities, non-redeemable preferred stock [Member]
Investment disclosure details
Equity securities, cost	167	174
Gross unrealized gains	30	46
Gross unrealized losses	3	5
Equity securities, at fair value	194	215
Continuous unrealized loss position less than 12 months, fair value	58	45
Continuous unrealized loss position less than 12 months, gross unrealized losses	1	1
Continuous unrealized loss position 12 months or longer, fair value	35	49
Continuous unrealized loss position 12 months or longer, gross unrealized losses	2	4
Continuous unrealized loss position, total, fair value	93	94
Continuous unrealized loss position, total, gross unrealized losses	$ 3	$ 5