Insurance (Obligations Under Funding Agreements - Liability and Collateral) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Federal Home Loan Bank amount of advances by branch for funding agreements	$ 300	$ 0
Collateral pledged relating to obligations under funding agreements	564
Fixed and Floating Rate Funding Agreements by Type [Line Items]
Outstanding funding agreements to certain SPEs	34,200	30,800
Invested Assets Pledged As Collateral	24,174	23,882
Funding agreements - Federal Agricultural Mortgage Corporation
Fixed and Floating Rate Funding Agreements by Type [Line Items]
Outstanding funding agreements to certain SPEs	2,550	2,550
Invested Assets Pledged As Collateral	2,644	2,645
Federal Home Loan Bank of New York
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Federal Home Loan Bank amount of advances by branch for funding agreements	14,445	14,445
Collateral pledged relating to obligations under funding agreements	16,605	16,828
Federal Home Loan Bank of Des Moines
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Federal Home Loan Bank amount of advances by branch for funding agreements	625	625
Collateral pledged relating to obligations under funding agreements	701	811
Federal Home Loan Bank of Pittsburgh
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Federal Home Loan Bank amount of advances by branch for funding agreements	250	250
Collateral pledged relating to obligations under funding agreements	$ 311	$ 383