Investments (Details 32) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	$ 481	$ 664
Provision (release)	35	39
Charge-offs, net of recoveries	0	4
Ending Balance	446	621
Commercial mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	398	562
Provision (release)	30	30
Charge-offs, net of recoveries	0	0
Ending Balance	368	532
Agricultural mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	81	88
Provision (release)	6	9
Charge-offs, net of recoveries	0	3
Ending Balance	75	76
Residential mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	2	14
Provision (release)	(1)	0
Charge-offs, net of recoveries	0	1
Ending Balance	$ 3	$ 13