Investments (Maturities of Fixed Maturity Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 1,873
Amortized Cost, Due after one year through five years	6,610
Amortized Cost, Due after five years through ten years	12,382
Amortized Cost, Due after ten years	25,537
Amortized Cost, Structured Securities	15,736
Amortized Cost	62,138	$ 59,672
Estimated Fair Value, Due in one year or less	1,877
Estimated Fair Value, Due after one year through five years	6,803
Estimated Fair Value, Due after five years through ten years	13,211
Estimated Fair Value, Due after ten years	31,189
Estimated Fair Value, Structured Securities	16,596
Fixed maturity securities	$ 69,676	$ 61,348