Investments, Available-for-Sale Fixed Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Cost or Amortized Cost [Abstract]
Cost or amortized cost	$ 38,059	$ 38,157
Estimated Fair Value [Abstract]
Estimated fair value	40,124	42,240
Available-for-Sale Fixed Maturities [Member]
Cost or Amortized Cost [Abstract]
Due in one year or less	1,331	1,334
Due after one year through five years	11,554	9,746
Due after five years through ten years	13,078	14,892
Due after ten years	12,056	12,134
Cost or amortized cost	38,019	38,106
Estimated Fair Value [Abstract]
Due in one year or less	1,325	1,356
Due after one year through five years	11,812	10,186
Due after five years through ten years	13,069	15,931
Due after ten years	13,877	14,714
Estimated fair value	$ 40,083	$ 42,187