Investments (AFS securities aggregated by investment category and length of time) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
Less Than or Equal to Twelve Months	$ 3,343	$ 3,993
Greater Than Twelve Months	1,616	2,490
Continuous Unrealized Loss Position, Total	4,959	6,483
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses and OTTI
Less Than or Equal to Twelve Months	214	338
Greater Than Twelve Months	301	771
Gross Unrealized Losses and OTTI, Total	515	1,109
Available For Sale Securities In Unrealized Loss Position Qualitative Disclosure Number Of Positions	626	897
Corporate bonds [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
Less Than or Equal to Twelve Months	2,853	2,848
Greater Than Twelve Months	934	1,452
Continuous Unrealized Loss Position, Total	3,787	4,300
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses and OTTI
Less Than or Equal to Twelve Months	145	162
Greater Than Twelve Months	182	423
Gross Unrealized Losses and OTTI, Total	327	585
RMBS [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
Less Than or Equal to Twelve Months	272	565
Greater Than Twelve Months	199	429
Continuous Unrealized Loss Position, Total	471	994
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses and OTTI
Less Than or Equal to Twelve Months	39	125
Greater Than Twelve Months	24	74
Gross Unrealized Losses and OTTI, Total	63	199
CMBS [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
Less Than or Equal to Twelve Months	66	178
Greater Than Twelve Months	113	146
Continuous Unrealized Loss Position, Total	179	324
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses and OTTI
Less Than or Equal to Twelve Months	16	15
Greater Than Twelve Months	19	100
Gross Unrealized Losses and OTTI, Total	35	115
CDOs [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
Less Than or Equal to Twelve Months	10	9
Greater Than Twelve Months	53	80
Continuous Unrealized Loss Position, Total	63	89
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses and OTTI
Less Than or Equal to Twelve Months	8	1
Greater Than Twelve Months	3	18
Gross Unrealized Losses and OTTI, Total	11	19
State and municipal bonds [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
Less Than or Equal to Twelve Months	64	31
Greater Than Twelve Months	24	30
Continuous Unrealized Loss Position, Total	88	61
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses and OTTI
Less Than or Equal to Twelve Months	1	0
Greater Than Twelve Months	6	9
Gross Unrealized Losses and OTTI, Total	7	9
Hybrid and redeemable preferred securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
Less Than or Equal to Twelve Months	71	324
Greater Than Twelve Months	293	353
Continuous Unrealized Loss Position, Total	364	677
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses and OTTI
Less Than or Equal to Twelve Months	3	23
Greater Than Twelve Months	67	147
Gross Unrealized Losses and OTTI, Total	70	170
Fixed maturity securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
Less Than or Equal to Twelve Months	3,336	3,955
Greater Than Twelve Months	1,616	2,490
Continuous Unrealized Loss Position, Total	4,952	6,445
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses and OTTI
Less Than or Equal to Twelve Months	212	326
Greater Than Twelve Months	301	771
Gross Unrealized Losses and OTTI, Total	513	1,097
Available-for-sale equity securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
Less Than or Equal to Twelve Months	7	38
Greater Than Twelve Months	0	0
Continuous Unrealized Loss Position, Total	7	38
Available-for-sale Securities, Continuous Unrealized Loss Position, Gross Unrealized Losses and OTTI
Less Than or Equal to Twelve Months	2	12
Greater Than Twelve Months	0	0
Gross Unrealized Losses and OTTI, Total	$ 2	$ 12