Investments (Continuous Gross Unrealized Losses for Fixed Maturity and Equity Securities Available-For-Sale) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Total number of securities in an unrealized loss position less than 12 months	1,128	327
Total number of securities in an unrealized loss position equal to or greater than 12 months	310	420
Fixed maturity securities [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	$ 10,584	$ 1,967
Less than 12 Months Gross Unrealized Loss	426	36
Equal to or Greater than 12 Months Estimated Fair Value	1,335	2,027
Equal to or Greater than 12 Months Gross Unrealized Loss	168	239
U.S. corporate securities [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	2,790	784
Less than 12 Months Gross Unrealized Loss	144	16
Equal to or Greater than 12 Months Estimated Fair Value	415	621
Equal to or Greater than 12 Months Gross Unrealized Loss	51	66
U.S. Treasury and agency securities [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	3,254	200
Less than 12 Months Gross Unrealized Loss	125	0
Equal to or Greater than 12 Months Estimated Fair Value	0	0
Equal to or Greater than 12 Months Gross Unrealized Loss	0	0
Foreign corporate securities [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	1,778	494
Less than 12 Months Gross Unrealized Loss	76	8
Equal to or Greater than 12 Months Estimated Fair Value	133	203
Equal to or Greater than 12 Months Gross Unrealized Loss	13	18
RMBS [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	1,419	62
Less than 12 Months Gross Unrealized Loss	42	6
Equal to or Greater than 12 Months Estimated Fair Value	494	781
Equal to or Greater than 12 Months Gross Unrealized Loss	78	108
ABS [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	713	208
Less than 12 Months Gross Unrealized Loss	3	1
Equal to or Greater than 12 Months Estimated Fair Value	195	266
Equal to or Greater than 12 Months Gross Unrealized Loss	10	17
State and political subdivision securities [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	267	44
Less than 12 Months Gross Unrealized Loss	17	2
Equal to or Greater than 12 Months Estimated Fair Value	52	55
Equal to or Greater than 12 Months Gross Unrealized Loss	14	25
CMBS [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	170	59
Less than 12 Months Gross Unrealized Loss	4	1
Equal to or Greater than 12 Months Estimated Fair Value	46	101
Equal to or Greater than 12 Months Gross Unrealized Loss	2	5
Foreign government debt securities [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	193	116
Less than 12 Months Gross Unrealized Loss	15	2
Equal to or Greater than 12 Months Estimated Fair Value	0	0
Equal to or Greater than 12 Months Gross Unrealized Loss	0	0
Equity Securities [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	129	10
Less than 12 Months Gross Unrealized Loss	9	1
Equal to or Greater than 12 Months Estimated Fair Value	45	57
Equal to or Greater than 12 Months Gross Unrealized Loss	10	22
Common Stock [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	3	10
Less than 12 Months Gross Unrealized Loss	3	1
Equal to or Greater than 12 Months Estimated Fair Value	7	7
Equal to or Greater than 12 Months Gross Unrealized Loss	0	0
Non-redeemable preferred stock [Member]
Continuous Gross Unrealized Loss and OTTI Loss for Fixed Maturity and Equity Securities Available-for-Sale
Less than 12 months Estimated Fair Value	126	0
Less than 12 Months Gross Unrealized Loss	6	0
Equal to or Greater than 12 Months Estimated Fair Value	38	50
Equal to or Greater than 12 Months Gross Unrealized Loss	$ 10	$ 22