Investments Investments (Past Due and Interest Accrual Status of Mortgage Loans) (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	$ 26,000,000	$ 11,000,000
Nonaccrual	26,000,000	11,000,000
Commercial
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	0	0
Nonaccrual	0	0
Agricultural
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	0	0
Nonaccrual	0	0
Residential
Financing Receivable, Recorded Investment, Aging [Abstract]
Past Due	26,000,000	11,000,000
Nonaccrual	$ 26,000,000	$ 11,000,000