Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	$ 305	$ 322
Provision (release)	32	12
Charge-offs, net of recoveries	(26)	(27)
Balance, end of period	311	307
Commercial
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	224	258
Provision (release)	3	(8)
Charge-offs, net of recoveries	(12)	(23)
Balance, end of period	215	227
Agricultural
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	39	44
Provision (release)	2	(5)
Charge-offs, net of recoveries	0	(1)
Balance, end of period	41	38
Residential
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	42	20
Provision (release)	27	25
Charge-offs, net of recoveries	(14)	(3)
Balance, end of period	$ 55	$ 42