Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Mortgage Loans on Real Estate [Line Items]
Beginning Balance	$ 302	$ 361	$ 347	$ 481
Provision (release)	24	8	(11)	(90)
Charge-offs, net of recoveries	0	(10)	(10)	(26)
Transfers to held-for-sale	0	(5)	0	(11)
Ending Balance	326	354	326	354
Commercial mortgage loans portfolio segment [Member]
Mortgage Loans on Real Estate [Line Items]
Beginning Balance	242	300	293	398
Provision (release)	17	2	(34)	(96)
Charge-offs, net of recoveries	0	(2)	0	(2)
Transfers to held-for-sale	0	0	0	0
Ending Balance	259	300	259	300
Agricultural [Member]
Mortgage Loans on Real Estate [Line Items]
Beginning Balance	49	59	52	81
Provision (release)	1	6	8	0
Charge-offs, net of recoveries	0	(8)	(10)	(24)
Transfers to held-for-sale	0	(5)	0	(5)
Ending Balance	50	52	50	52
Residential [Member]
Mortgage Loans on Real Estate [Line Items]
Beginning Balance	11	2	2	2
Provision (release)	6	0	15	6
Charge-offs, net of recoveries	0	0	0	0
Transfers to held-for-sale	0	0	0	(6)
Ending Balance	$ 17	$ 2	$ 17	$ 2