Investments (Valuation Allowance Rollforward by Portfolio Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	$ 318	$ 305
Provision (release)	68	15
Charge-offs, net of recoveries	(5)	(5)
Balance, end of period	381	315
Commercial
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	217	224
Provision (release)	64	1
Charge-offs, net of recoveries	0	0
Balance, end of period	281	225
Agricultural
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	42	39
Provision (release)	0	0
Charge-offs, net of recoveries	(2)	0
Balance, end of period	40	39
Residential
Mortgage Loans on Real Estate [Line Items]
Balance, beginning of period	59	42
Provision (release)	4	14
Charge-offs, net of recoveries	(3)	(5)
Balance, end of period	$ 60	$ 51