Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	$ 332	$ 446	$ 347	$ 481
Provision (release)	(24)	(63)	(35)	(98)
Charge-offs, net of recoveries	(6)	(16)	(10)	(16)
Transfers to held-for-sale	0	(6)	0	(6)
Ending Balance	302	361	302	361
Commercial mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	275	368	293	398
Provision (release)	(33)	(68)	(51)	(98)
Charge-offs, net of recoveries	0	0	0	0
Transfers to held-for-sale	0	0	0	0
Ending Balance	242	300	242	300
Agricultural [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	54	75	52	81
Provision (release)	1	0	7	(6)
Charge-offs, net of recoveries	(6)	(16)	(10)	(16)
Transfers to held-for-sale	0	0	0	0
Ending Balance	49	59	49	59
Residential [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	3	3	2	2
Provision (release)	8	5	9	6
Charge-offs, net of recoveries	0	0	0	0
Transfers to held-for-sale	0	(6)	0	(6)
Ending Balance	$ 11	$ 2	$ 11	$ 2