Investments, Available-for-Sale Fixed Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Cost or Amortized Cost [Abstract]
Cost or amortized cost	$ 40,342	$ 38,963
Estimated Fair Value [Abstract]
Estimated fair value	45,069	44,646
Available-for-Sale Fixed Maturities [Member]
Cost or Amortized Cost [Abstract]
Due in one year or less	1,648	1,456
Due after one year through five years	10,776	12,304
Due after five years through ten years	13,628	12,319
Due after ten years	14,281	12,847
Cost or amortized cost	40,333	38,926
Estimated Fair Value [Abstract]
Due in one year or less	1,656	1,458
Due after one year through five years	11,517	13,098
Due after five years through ten years	14,794	13,878
Due after ten years	17,093	16,170
Estimated fair value	$ 45,060	$ 44,604