Investments (Maturities of Fixed Maturity Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Available-for-sale Securities, Debt Maturities [Abstract]
Amortized Cost, Due in one year or less	$ 12,704
Amortized Cost, Due after one year through five years	54,663
Amortized Cost, Due after five years through ten years	59,986
Amortized Cost, Due after ten years	110,457
Amortized Cost, RMBS, CMBS and ABS	49,006
Amortized Cost, Subtotal	286,816	$ 286,069
Estimated Fair Value, Due in one year or less	12,734
Estimated Fair Value, Due after one year through five years	55,876
Estimated Fair Value, Due after five years through ten years	61,116
Estimated Fair Value, Due after ten years	119,068
Estimated fair value, Mortgage-backed and asset-backed securities	49,471
Debt Securities, Available-for-sale	$ 298,265	$ 308,931