Investments, Available-for-Sale Fixed Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Cost or Amortized Cost [Abstract]
Cost or amortized cost	$ 38,979	$ 38,157
Estimated Fair Value [Abstract]
Estimated fair value	43,917	42,240
Available-for-Sale Fixed Maturities [Member]
Cost or Amortized Cost [Abstract]
Due in one year or less	1,372	1,334
Due after one year through five years	11,955	9,746
Due after five years through ten years	13,026	14,892
Due after ten years	12,609	12,134
Cost or amortized cost	38,962	38,106
Estimated Fair Value [Abstract]
Due in one year or less	1,392	1,356
Due after one year through five years	12,625	10,186
Due after five years through ten years	14,359	15,931
Due after ten years	15,518	14,714
Estimated fair value	$ 43,894	$ 42,187