Investments (Past Due and Interest Accrual Status of Mortgage Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	$ 618	$ 684
Greater than 90 Days Past Due and Still Accruing Interest	80	153
Nonaccrual	724	717
Agricultural Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	134	204
Greater than 90 Days Past Due and Still Accruing Interest	39	109
Nonaccrual	105	105
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	1	9
Greater than 90 Days Past Due and Still Accruing Interest	1	9
Nonaccrual	176	176
Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Past Due	483	471
Greater than 90 Days Past Due and Still Accruing Interest	40	35
Nonaccrual	$ 443	$ 436