Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Premiums Earned, Net [Abstract]
Direct	$ 69,711	$ 62,968	$ 8,365
Assumed	478	2,108	38
Ceded	(825)	(1,954)	(219)
Net premiums	69,364	63,122	8,184
Policyholder Benefits and Claims Incurred, Net [Abstract]
Direct	56,077	52,592	6,773
Assumed	329	1,562	32
Ceded	(727)	(1,625)	(211)
Net benefit costs	$ 55,679	$ 52,529	$ 6,594

Amount of earned premiums assumed from other entities.

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