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	$ 1,512
Amortized Cost, Due after one year through five years	7,643
Amortized Cost, Due after five years through ten years	11,380
Amortized Cost, Due after ten years	23,531
Amortized Cost, Structured Securities	15,606
Amortized Cost, Subtotal	59,672	$ 58,599
Estimated Fair Value, Due in one year or less	1,512
Estimated Fair Value, Due after one year through five years	7,661
Estimated Fair Value, Due after five years through ten years	11,170
Estimated Fair Value, Due after ten years	25,326
Estimated Fair Value, Structured Securities	15,679
Debt Securities, Available-for-sale	$ 61,348	$ 63,333