Investments and Derivative Instruments (Details 8) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012 Commercial [Member]	Dec. 31, 2011 Commercial [Member]	Sep. 30, 2012 Greater than 80% [Member] Commercial [Member]	Dec. 31, 2011 Greater than 80% [Member] Commercial [Member]	Sep. 30, 2012 65% - 80% [Member] Commercial [Member]	Dec. 31, 2011 65% - 80% [Member] Commercial [Member]	Sep. 30, 2012 Less than 65% [Member] Commercial [Member]	Dec. 31, 2011 Less than 65% [Member] Commercial [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Document Period End Date	Sep. 30, 2012
Commercial Mortgage Loans Credit Quality
Carrying Value		$ 6,863	$ 5,728	$ 372	$ 707	$ 2,569	$ 2,384	$ 3,922	$ 2,637
Avg. Debt-Service Coverage Ratio	2.29	2.29	1.94	1.54	1.45	2.12	1.60	2.49	2.40