Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	$ 305	$ 322
Provision (release)	15	5
Charge-offs, net of recoveries	(5)	(1)
Balance, end of period	315	326
Commercial
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	224	258
Provision (release)	1	1
Charge-offs, net of recoveries	0	0
Balance, end of period	225	259
Agricultural
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	39	44
Provision (release)	0	(2)
Charge-offs, net of recoveries	0	0
Balance, end of period	39	42
Residential
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	42	20
Provision (release)	14	6
Charge-offs, net of recoveries	(5)	(1)
Balance, end of period	$ 51	$ 25