Investments and Derivative Instruments (Details 9) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Document Period End Date	Mar. 31, 2013
Carrying Value	$ 5,229	$ 6,711
Percent of Total	100.00%	100.00%
East North Central [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	128	145
Percent of Total	2.40%	2.20%
Middle Atlantic [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	315	477
Percent of Total	6.00%	7.10%
Mountain [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	78	99
Percent of Total	1.50%	1.50%
New England [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	266	350
Percent of Total	5.10%	5.20%
Pacific [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	1,510	1,978
Percent of Total	28.90%	29.50%
South Atlantic [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	853	1,378
Percent of Total	16.30%	20.50%
West North Central [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	16	16
Percent of Total	0.30%	0.20%
West South Central [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	336	398
Percent of Total	6.40%	5.90%
Other [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	$ 1,727	$ 1,870
Percent of Total	33.10%	27.90%