Investments (Details 38) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Mar. 31, 2011
Financing Receivable, Modifications [Line Items]
Number of Mortgage Loans	0	3
Pre-Modification	$ 0	$ 63
Post-Modification	0	66
Commercial
Financing Receivable, Modifications [Line Items]
Number of Mortgage Loans	0	1
Pre-Modification	0	53
Post-Modification	0	55
Agricultural
Financing Receivable, Modifications [Line Items]
Number of Mortgage Loans	0	2
Pre-Modification	0	10
Post-Modification	0	11
Residential
Financing Receivable, Modifications [Line Items]
Number of Mortgage Loans	0	0
Pre-Modification	0	0
Post-Modification	$ 0	$ 0