Investments, Available-for-Sale Fixed Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Cost or Amortized Cost [Abstract]
Cost or amortized cost	$ 39,293	$ 38,963
Estimated Fair Value [Abstract]
Estimated fair value	43,584	44,646
Available-for-Sale Fixed Maturities [Member]
Cost or Amortized Cost [Abstract]
Due in one year or less	1,468	1,456
Due after one year through five years	10,837	12,304
Due after five years through ten years	13,640	12,319
Due after ten years	13,312	12,847
Cost or amortized cost	39,257	38,926
Estimated Fair Value [Abstract]
Due in one year or less	1,473	1,458
Due after one year through five years	11,583	13,098
Due after five years through ten years	14,685	13,878
Due after ten years	15,804	16,170
Estimated fair value	$ 43,545	$ 44,604