Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	$ 318	$ 305
Provision (release)	158	29
Charge-offs, net of recoveries	(9)	(9)
Balance, end of period	467	325
Commercial
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	217	224
Provision (release)	150	4
Charge-offs, net of recoveries	0	0
Balance, end of period	367	228
Agricultural
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	42	39
Provision (release)	1	2
Charge-offs, net of recoveries	(2)	0
Balance, end of period	41	41
Residential
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	59	42
Provision (release)	7	23
Charge-offs, net of recoveries	(7)	(9)
Balance, end of period	$ 59	$ 56