Investments and Derivative Instruments (Details 9) (USD $) In Millions, unless otherwise specified	Jun. 30, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	$ 5,304	$ 4,489
Percent of Total	100.00%	100.00%
East North Central [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	76	77
Percent of Total	1.40%	1.70%
Middle Atlantic [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	498	428
Percent of Total	9.40%	9.50%
Mountain [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	127	109
Percent of Total	2.40%	2.40%
New England [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	296	259
Percent of Total	5.60%	5.80%
Pacific [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	1,307	1,147
Percent of Total	24.60%	25.60%
South Atlantic [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	1,150	1,177
Percent of Total	21.70%	26.30%
West North Central [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	34	36
Percent of Total	0.60%	0.80%
West South Central [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	225	231
Percent of Total	4.20%	5.10%
Other [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	$ 1,591	$ 1,025
Percent of Total	30.10%	22.80%