Investments and Derivative Instruments (Details 8) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Commercial [Member]	Dec. 31, 2012 Commercial [Member]	Mar. 31, 2013 Greater than 80% [Member] Commercial [Member]	Dec. 31, 2012 Greater than 80% [Member] Commercial [Member]	Mar. 31, 2013 65% - 80% [Member] Commercial [Member]	Dec. 31, 2012 65% - 80% [Member] Commercial [Member]	Mar. 31, 2013 Less than 65% [Member] Commercial [Member]	Dec. 31, 2012 Less than 65% [Member] Commercial [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Document Period End Date	Mar. 31, 2013
Commercial Mortgage Loans Credit Quality
Carrying Value		$ 5,229	$ 6,711	$ 203	$ 253	$ 1,506	$ 2,220	$ 3,520	$ 4,238
Avg. Debt-Service Coverage Ratio	2.08	2.08	2.24	0.97	0.95	1.94	2.12	2.22	2.40