Investments (Details 38) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Financing Receivable, Modifications [Line Items]
Number of Mortgage Loans	5	8	5	17
Pre-Modification	$ 17	$ 99	$ 17	$ 184
Post-Modification	16	60	16	147
Commercial
Financing Receivable, Modifications [Line Items]
Number of Mortgage Loans	0	3	0	5
Pre-Modification	0	88	0	147
Post-Modification	0	49	0	109
Agricultural
Financing Receivable, Modifications [Line Items]
Number of Mortgage Loans	5	2	5	9
Pre-Modification	17	10	17	36
Post-Modification	16	10	16	37
Residential
Financing Receivable, Modifications [Line Items]
Number of Mortgage Loans	0	3	0	3
Pre-Modification	0	1	0	1
Post-Modification	$ 0	$ 1	$ 0	$ 1