Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	$ 347	$ 481
Provision (release)	(11)	(35)
Charge-offs, net of recoveries	(4)	0
Ending Balance	332	446
Commercial mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	293	398
Provision (release)	(18)	(30)
Charge-offs, net of recoveries	0	0
Ending Balance	275	368
Agricultural [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	52	81
Provision (release)	6	(6)
Charge-offs, net of recoveries	(4)	0
Ending Balance	54	75
Residential [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	2	2
Provision (release)	1	1
Charge-offs, net of recoveries	0	0
Ending Balance	$ 3	$ 3