Investments (Maturities of Fixed Maturity Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Amortized Cost, Due in one year or less	$ 1,682
Amortized Cost, Due after one year through five years	6,815
Amortized Cost, Due after five years through ten years	12,485
Amortized Cost, Due after ten years	26,101
Amortized Cost, Structured Securities	16,000
Amortized Cost	63,083	$ 59,672
Estimated Fair Value, Due in one year or less	1,691
Estimated Fair Value, Due after one year through five years	7,038
Estimated Fair Value, Due after five years through ten years	13,343
Estimated Fair Value, Due after ten years	31,211
Estimated Fair Value, Structured Securities	16,694
Estimated Fair Value	$ 69,977	$ 61,348