Investments (Details 5) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	$ 481	$ 664	$ 721
Provision (release)	(86)	(145)	9
Charge-offs, net of recoveries	(37)	(19)	(66)
Transfers to held-for-sale	(11)	(19)
Ending Balance	347	481	664
Commercial mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	398	562	589
Provision (release)	(92)	(152)	(5)
Charge-offs, net of recoveries	(13)	(12)	(22)
Transfers to held-for-sale	0	0
Ending Balance	293	398	562
Agricultural mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	81	88	115
Provision (release)	0	(3)	12
Charge-offs, net of recoveries	(24)	(4)	(39)
Transfers to held-for-sale	(5)	0
Ending Balance	52	81	88
Residential mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	2	14	17
Provision (release)	6	10	2
Charge-offs, net of recoveries	0	(3)	(5)
Transfers to held-for-sale	(6)	(19)
Ending Balance	$ 2	$ 2	$ 14