Investments (Past Due and Interest Accrual Status of Mortgage Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	$ 444	$ 431
Nonaccrual Status	345	364
Commercial
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	0	2
Nonaccrual Status	0	0
Agricultural
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	127	103
Nonaccrual Status	40	46
Residential
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	317	326
Nonaccrual Status	$ 305	$ 318