Investments (Details 32) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	$ 361	$ 566	$ 481	$ 664
Provision (release)	8	(36)	(90)	(130)
Charge-offs, net of recoveries	(10)	(1)	(26)	(5)
Transfers to held-for-sale	(5)		(11)
Ending Balance	354	529	354	529
Commercial mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	300	469	398	562
Provision (release)	2	(41)	(96)	(134)
Charge-offs, net of recoveries	(2)	0	(2)	0
Transfers to held-for-sale	0		0
Ending Balance	300	428	300	428
Agricultural mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	59	79	81	88
Provision (release)	6	3	0	(3)
Charge-offs, net of recoveries	(8)	0	(24)	(3)
Transfers to held-for-sale	(5)		(5)
Ending Balance	52	82	52	82
Residential mortgage loans portfolio segment [Member]
Allowance for Loan and Lease Losses, Provision for Loss, Net
Beginning Balance	2	18	2	14
Provision (release)	0	2	6	7
Charge-offs, net of recoveries	0	(1)	0	(2)
Transfers to held-for-sale	0		(6)
Ending Balance	$ 2	$ 19	$ 2	$ 19